C++ 计算机程序设计（西安交大mooc）

　　第一周 基础练习

　　1、显示Hello World!

#include <iostream>
using namespace std;
int main()
{
    cout << "Hello World!" << endl;
    return 0;
}

　　2、显示唐诗

#include <iostream>
using namespace std;
int main()
{
    cout<<  "慈母手中线
"
            "游子身上衣
"
            "临行密密缝
"
            "意恐迟迟归
"
            "谁言寸草心
"
            "报得三春晖
";
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    cout<< "慈母手中线

游子身上衣

临行密密缝

意恐迟迟归

谁言寸草心

报得三春晖" << endl;    
    return 0;
}

　　3、显示一句话

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string name;
    cin >> name;
    cout << "This program is coded by " + name + "." << endl;
    return 0;
}

　　4、还是一句话，getline(cin,name); 是string类重载的友元函数；cin.getline()是istream类的成员函数

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string name;
    getline(cin,name);
    cout << "This program is coded by " + name + "." << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    char name[20];
    /* 从键盘输入字符时，字符一直在键盘缓冲区中(shell缓冲区)，
    当在键盘输入'
'时，键盘缓冲区中的字符才被全部传送到stdin缓冲区中 */
    cin >> name;
    cout << name << endl;
    
    cin >> name;  /* 忽略空白符 缓冲区还剩余一个回车*/
    cout << name << endl;
    
    cin.sync();   /* 清空缓冲区 */
    
    /* 可以读取空白符'
' 以回车作为结束标记并且读取回车符 缓冲区没有剩余*/
    cin.getline(name, 15); 
    cout << name << endl;
    
    cout << getchar() << endl;  /* 缓冲区是空的 等待输入 */
    return 0;
}

　　5、计算矩形周长

#include <iostream>
using namespace std;
int main()
{
    int a, b;
    cin >> a >> b;
    cout << 2 * ( a + b ) << endl;
    return 0;
}

　　6、已知直角边求斜边

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double a, b, c;
    cin >> a >> b;
    cout << sqrt ( a*a + b*b ) << endl;
    return 0;
}

　　第一周 中级练习

　　1、计算公式的值(对数)，以m为底的n的对数 log(n) / log(m)

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double x, a;
    cin >> x >> a;
    cout << log(x+sqrt(x*x+1)) / log(a) << endl;
    return 0;
} 

　　2、e的近似值

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double n;
    cin >> n;
    cout << pow(1+1/n, n) << endl;
    return 0;
} 

#include <iostream>
using namespace std;
int main()
{
    int n, t;
    double y = 1.0;
    cin >> n;
    
    t = n;
    while(t--)
    {
        y *= (1+1.0/n);
    }
    
    cout << y << endl;
    return 0;
} 

　　3、计算公式的值（三角等）

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double x;
    cin >> x;
    cout << sin(x) - log(x) + sqrt(x) - 5 << endl;
    return 0;
} 

　　4、计算公式的值（开方）

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double x;
    cin >> x;
    cout << x / sqrt(x*x-3*x+2) << endl;
    return 0;
} 

　　第一周 编程作业

　　1、1-1我爱C++

#include <iostream>
using namespace std;
int main()
{
    cout << "Hello C++." << endl;
    cout << "I like programming." << endl;
    return 0;
}

　　2、1-2来自系统的问候，注意字符数组的长度

#include <iostream>
using namespace std;
int main()
{
    char name[256];
    cin.getline( name, 35 );
    cout << "Hello " << name << "." << endl;
    return 0;
}

　　3、1-3乘法计算器

#include <iostream>
using namespace std;
int main()
{
    double a, b;
    cin >> a >> b;
    cout << a * b << endl;
    return 0;
}

　　4、1-4单位换算

#include <iostream>
using namespace std;
int main()
{
    double inch;
    const double inch_to_cm = 2.54;
    cin >> inch;
    cout << inch << "inch=" << inch * inch_to_cm << "cm" << endl;
    return 0;
}

　　5、1-5平方根计算器

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double x;
    cin >> x;
    cout << sqrt(x) << endl;
    return 0;
}

　　第二周 基础练习

　　1、求过平面上两点的直线的斜率，斜率 ( y1 - y2 ) / ( x1 - x2 ) 

#include <iostream>
using namespace std;
int main()
{
    double x1, y1 , x2, y2;
    cin >> x1 >> y1 >> x2 >> y2;
    cout << ( y1 - y2 ) / ( x1 - x2 ) << endl;
    return 0;
} 

　　2、计算平面上两点之间的距离

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double x1, y1 , x2, y2, distance;
    cin >> x1 >> y1 >> x2 >> y2;
    distance = sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
    cout << distance << endl;
    return 0;
} 

　　3、判断大小写

#include <iostream>
using namespace std;
int main()
{
    char ch;
    cin >> ch;
    if(ch >= 'A' && ch <= 'Z')
        cout << 1 << endl;
    else
        cout << 0 << endl;
    return 0;
} 

　　4、判断数字

#include <iostream>
using namespace std;
int main()
{
    char ch;
    cin >> ch;
    if(ch >= '0' && ch <= '9')
        cout << 1 << endl;
    else
        cout << 0 << endl;
    return 0;
} 

　　5、判断闰年

#include <iostream>
using namespace std;
int main()
{
    int year;
    cin >> year;
    if(year%4==0&&year%100!=0||year%400==0)
        cout << "IsLeapYear" << endl;
    else
        cout << "NotLeapYear" << endl;
    return 0;
} 

　　6、求商和余数

#include <iostream>
using namespace std;
int main()
{
    int a, b;
    cin >> a >> b;
    cout << a/b << " " << a%b << endl;
    return 0;
} 

　　7、计算平均分取整

#include <iostream>
using namespace std;
int main()
{
    int x, y, sum = 0, n = 7;
    
    while(n--)
    {
        cin >> x;
        sum += x;
    }
    
    y = int( sum/7.0 + 0.5 );
    cout << y << endl;
    return 0;
} 

　　8、计算点到直线的距离保留两位小数，int( d*100 + 0.5 ) / 100.0

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    int A, B, C, x, y;
    cin >> A >> B >> C;
    cin >> x >> y;
    
    double d = fabs(A*x+B*y+C) / sqrt(A*A+B*B);
    
    cout <<  int( d*100 + 0.5 ) / 100.0 << endl;
    return 0;
} 

　　9、输入字符显示ASCII值，int(ch)

#include <iostream>
using namespace std;
int main()
{
    char ch;
    cin >> ch;
    cout << int(ch) << endl;
    return 0;
} 

　　10、输入整数显示ASCII字符

#include <iostream>
using namespace std;
int main()
{
    int k;
    cin >> k;
    cout << char(k) << endl;
    return 0;
} 

　　11、输入整数显示十六进制

#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    cout << hex << n << endl;
    return 0;
} 

　　12、输入整数显示十六进制和八进制，int sign = n < 0 ? (n = -n, -1) : 1;

#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    
    int sign = n < 0 ? (n = -n, -1) : 1;
    
    if(sign == -1){
        cout << n*sign << " -" << hex << n << " -"<< oct << n << endl;
    }
    else{
        cout << n << " " << hex << n << " "<< oct << n << endl;
    }
    return 0;
} 

#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;    
    
    int sign = n < 0 ? (n = -n, -1) : 1;
    
    sign == -1 ? cout << n*sign << " -" << hex << n << " -"<< oct << n << endl    
        : cout << n << " " << hex << n << " "<< oct << n << endl;
    return 0;
} 

　　第二周 中级练习

　　1、加密

#include <iostream>
using namespace std;
int main()
{
    char a, b, c, d;
    cin >> a >> b >> c >> d;
    (a-'a'>10) ? cout << a-'a' : cout << '0' << a-'a';
    (b-'a'>10) ? cout << b-'a' : cout << '0' << b-'a';
    (c-'a'>10) ? cout << c-'a' : cout << '0' << c-'a';
    (d-'a'>10) ? cout << d-'a' : cout << '0' << d-'a';
    cout << endl;
    return 0;
} 

#include <iostream>
using namespace std;
void fun(char a)
{
    (a-'a'>10) ? cout << a-'a' : cout << '0' << a-'a';
}
int main()
{
    char a, n = 4;
    while(n--)
    {
        cin >> a;
        fun(a);
    }
    cout << endl;
    return 0;
} 

　　2、解密

#include <iostream>
using namespace std;
int main()
{
    char a[256];
    cin >> a;
    for(int i=0; i<7; i += 2){
        cout << char((a[i]-'0')*10 + a[i+1]-'0' + 'a');
    }
    cout << endl;
    return 0;
} 

　　3、压缩存储，位移

#include <iostream>
using namespace std;
int main()
{
    int x = 0, a, b, c, d;
    cin >> a >> b >> c >> d;
    x = a << 24;
    x += b << 16;
    x += c <<8;
    x += d;
    cout << x << endl;
    return 0;
} 

#include <iostream>
using namespace std;
int main()
{
    int a, x = 0,  n = 4;
    
    while(n--)
    {
        cin >> a;
        x += (a << n*8);
    }
   
    cout << x << endl;
    return 0;
}

　　4、石头剪刀布

#include <iostream>
using namespace std;
int main()
{
    const char* answer[] = {"不认识", "石头", "剪刀", "布"};
    int i;
    cin >> i;
    (i >= 1 && i <= 3) ? cout << answer[i] : cout << answer[0];
    cout << endl;
    return 0;
}

　　5、排排坐分果果，格式要求，末尾无空格

#include <iostream>
using namespace std;
int main()
{
    int n = 4, a, k;
    cin >> a >> k;
    
    while(n--)
    {    
        ( n == 3 ) ? : cout << " ";
        (a = (a + k - 1)%10) ? cout << a : cout << "10";
        a = (a+1)%10;
    }
    
    cout << endl;
    return 0;
} 

　　第二周 编程作业

　　1、温度转换，小数常量默认是double类型

#include <iostream>
using namespace std;
int main()
{
    double C, F;
    cin >> F;
    C = 5.0/9*(F-32);
    cout << C << endl;
    return 0;
}

　　2、计算数学函数式的值

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double x, y;
    cin >> x;
    y = sin(x*x)/(1-cos(x));
    cout << y << endl;
    return 0;
}

　　3、数据的简单统计，题目要求，平均值的四舍五入整数值

#include <iostream>
using namespace std;
int main()
{
    int a, b, c;
    cin >> a >> b >> c;
    int sum = a + b + c;
    cout << sum << endl;
    cout << sum/3.0 << endl;
    int ave = sum/3.0 + 0.5;
    cout << ave << endl;
    return 0;
}

　　4、找零钱，格式最后没有空格

#include <iostream>
using namespace std;
int main()
{
    int x;
    cin >> x;
    
    cout << x/50 << " ";
    x %= 50;
    
    cout << x/20 << " ";
    x %= 20;
    
    cout << x/10 << " ";
    x %= 10;

    cout << x/5 << " ";
    x %= 5;
    
    cout << x << endl;
    return 0;
}

#include <iostream>
using namespace std;

void fun(int x){
    int arr[] = {50,20,10,5,1};
    for(int i=0; i<4; i++){
        cout << x/arr[i] << " ";
        x %= arr[i];
    }
    cout << x << endl;
}

int main()
{
    int x;
    cin >> x;
    fun(x);    
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    int x;
    cin >> x;
    int arr[] = {50,20,10,5,1};
    for(int i=0; i<5; i++){
        if(i) cout << " ";
        cout << x/arr[i];
        x %= arr[i];
    }
    return 0;
}

　　5、小写转大写，判断是否为小写字母

#include <iostream>
using namespace std;
int main()
{
    char ch;
    cin >> ch;
    if(ch >= 'a' && ch <= 'z')
        ch -= 32;
    cout.put(ch) << endl;    
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string s;
    cin >> s;
    if(s[0] >= 'a' && s[0] <= 'z')
        s[0] -= 32;
    cout << s[0] << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    char s[256];
    cin >> s;
    if(s[0] >= 'a' && s[0] <= 'z')
        s[0] -= 32;
    cout << s[0] << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    char ch;
    cin >> ch;
    if(ch >= 'a' && ch <= 'z')
        ch -= 32;
    cout<< ch << endl;    
    return 0;
}

　　第三周 基础练习

　　1、判断奇偶数

#include <iostream>
using namespace std;
int main()
{
    int x;
    cin >> x;
    if(x%2)
        cout << "odd" << endl;
    else
        cout << "even" << endl;
    return 0;
}

　　2、判断数的类型，int(x)==x，判断是否为整数

#include <iostream>
using namespace std;
int main()
{
    double x;
    cin >> x;
    switch(int(x)==x){ //是否为整数
        case 0:
            if(x>1e-6)
                cout << "positive real" << endl;
            else if(x<1e-6)
                cout << "negative real" << endl;
            else
                cout << "zero" << endl;
            break;
        case 1:
            if(int(x)>0)
                cout << "positive integer" << endl;
            else if(int(x)<0)
                cout << "negative integer" << endl;
            else
                cout << "zero" << endl;
            break;
    }
    return 0;
}

　　3、判断点的象限

#include <iostream>
using namespace std;
int main()
{
    double x, y;
    cin >> x >> y;
    if(x>1e-6 && y>1e-6)
        cout << 1 << endl;
    else if(x<1e-6 && y>1e-6)
        cout << 2 << endl;
    else if(x<1e-6 && y<1e-6)
        cout << 3 << endl;    
    else
        cout << 4 << endl;
    return 0;
}

　　4、判断字符类型

#include <iostream>
using namespace std;
int main()
{
    char ch;
    cin >> ch;
    if(ch>='0' && ch<='9')
        cout << 0 << endl;
    else if(ch>='A' && ch<='Z')
        cout << 1 << endl;
    else if(ch>='a' && ch<='z')
        cout << 2 << endl;    
    else
        cout << -1 << endl;
    return 0;
}

　　5、百分制成绩转五分制成绩

#include <iostream>
using namespace std;
int main()
{
    int x;
    cin >> x;
    switch(x/10){
        case 10:
        case 9:
            cout << 5 << endl;
            break;
        case 8:
            cout << 4 << endl;
            break;
        case 7:
            cout << 3 << endl;
            break;
        case 6:
            cout << 2 <<endl;
            break;
        case 5:case 4:case 3:case 2:case 1:
            cout << 1 << endl;
            break;
        default:
            cout << 0 << endl;
    }
    return 0;
}

　　6、显示n个字符

#include <iostream>
using namespace std;
int main()
{
    int n;
    char ch;
    cin >> n >> ch;
    while(n--)
        cout << ch;
    cout << endl;
    return 0;
}

　　7、显示字符组成的矩形

#include <iostream>
using namespace std;
int main()
{
    int n, m;
    char ch;
    cin >> m >> n >> ch;
    for(int i=0; i<m; ++i){
        for(int j=0; j<n; ++j)
            cout << ch;
        cout << endl;
    }
    return 0;
}

　　8、用循环计算1+2+3+...+n

#include <iostream>
using namespace std;
int main()
{
    int n, s = 0;
    cin >> n;
    for(int i=1; i<=n; ++i){
        s += i;
    }
    cout << s << endl;
    return 0;
}

　　9、计算1+1/2+1/3+...+1/n

#include <iostream>
using namespace std;
int main()
{
    int n;
    double s = 0;
    cin >> n;
    for(int i=1; i<=n; ++i){
        s += 1.0/i;
    }
    cout << s << endl;
    return 0;
}

　　10、计算n！，long fac = 1;

#include <iostream>
using namespace std;
int main()
{
    int n;
    long fac = 1;
    cin >> n;

    for(int i=1; i<=n; ++i){
        fac *= i;
    }
    cout << fac << endl;
    return 0;
}

　　11、交替输出1和-1

#include <iostream>
using namespace std;
int main()
{
    int n, sign = 1, t;
    cin >> n;
    t = n;
    while(n--)
    {
        if(n<t-1) cout << " ";  
        cout << sign;
        sign = -sign;
    }
    return 0;
}

　　12、判断整数的位数，n非负，即可以为0

#include <iostream>
using namespace std;
int main()
{
    int n, cnt=0;
    cin >> n;
    
    if(!n)
        cnt++;
    
    while(n)
    {
        n /= 10;
        cnt++;
    }
    
    cout << cnt << endl;
    return 0;
}

　　13、求非负整数的各位数字的和

#include <iostream>
using namespace std;
int main()
{
    int n, sum=0;
    cin >> n;
    
    while(n)
    {
        sum += n%10;
        n /= 10;
    }
    
    cout << sum << endl;
    return 0;
}

　　14、九九乘法表，行尾无空格

#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    
    for(int i=1; i<=n; ++i){
        for(int j=1; j<=i; ++j){        
            if(j>1)
                cout << " ";
            cout << i << "*" << j << "=" << i*j;
        }        
        cout << endl;
    }
    return 0;
}

　　15、不一样的九九乘法表

#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    
    for(int i=n; i>=1; --i){
        for(int j=1; j<=i; ++j){        
            if(j>1)
                cout << " ";
            cout << i << "*" << j << "=" << i*j;
        }        
        cout << endl;
    }
    return 0;
}

　　16、Fibonacci序列，输出n+1项

#include <iostream>
using namespace std;
int main()
{
    int n, f0 = 0, f1 = 1;
    cin >> n;
    for(int i=0; i<n+1; i++){
        if(i)
            cout << " ";
        cout << f0;
        int sum = f0 + f1;    
        f0 = f1;
        f1 = sum;            
    }
    return 0;
}

　　第三周 中级练习

　　1、计算1!+2!+3!+…+n!

#include <iostream>
using namespace std;
int main()
{
    int n, t = 1, result = 0;
    cin >> n;
    for(int i=1; i<=n; ++i){
        t *= i;
        result += t;
    }
    cout << result << endl;
    return 0;
} 

　　2、a+aa+aaa

#include <iostream>
using namespace std;
int main()
{
    int a, n, t = 0, result = 0;
    cin >> a >> n;
    for(int i=0; i<n; ++i){
        t = t*10 + a; //保存中间结果
        result += t;
    }
    cout << result << endl;
    return 0;
} 

　　3、arcsin(x)

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double x;
    cin >> x;
    
    int n = 0; //第0项
    double u = x, arcsin = 0;
    
    while(fabs(u)>=1e-8){            
        arcsin += u; //累加
        n++;         //从第一项开始计算u
        u =  u*(2*n-1)*(2*n-1)*x*x/2/n/(2*n+1);    
    }
    
    cout << arcsin << endl;
    return 0;
} 

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    double x;
    cin >> x;
    cout << asin(x) << endl;
    return 0;
} 

　　4、回文数

#include <iostream>
using namespace std;
int main()
{
    int n, t, sum = 0;
    cin >> n;
    t = n;
    
    while(t)
    {
        sum = sum*10 + t%10;
        t /= 10;
    }
    
    if(sum==n)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;        
    return 0;
} 

#include <iostream>
#include <string.h>
using namespace std;
int main()
{
    char str[256], *p, *q;
    cin >> str;
    p = str, q = str + strlen(str)-1; 
    
    while(*p==*q && p<q){
        p++,q--;
    }
    
    if(p>=q)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;        
    return 0;
}

#include <iostream>
#include <string.h>
using namespace std;
int main()
{
    char str[256], i, j;
    cin >> str;
    for(i=0, j=strlen(str)-1; str[i] == str[j] && i<j; ++i, --j);
    if(i>=j)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;        
    return 0;
}

　　5、整数的素数因子分解

#include <iostream>
using namespace std;
int main()
{
    int i=2, n;
    cin >> n;
    cout << n << "=";
    while(n>1)
    {        
        if(n%i==0){
            cout << i;
            n /= i;
            if(n>1)
            cout << "*"; /* */
        }
        else{
            i++;
        }                
    }    
    return 0;
} 

#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    cout << n << "=";
    for(int i=2; n>1; ++i)
    {        
        if(n%i==0){
            cout << i;
            n /= i;
            --i;
            if(n>1)
                cout << "*"; 
        }                
    }    
    return 0;
} 

　　第三周 编程作业

　　1、3-1打印3个相邻字母

#include <iostream>
using namespace std;
int main()
{
    char ch,ch1 = 'A';
    cin >> ch;
    if(ch>='a' && ch<='z')
        ch1 = 'a';
    cout << char((ch-ch1-1+26)%26+ch1) << ch << char((ch-ch1+1)%26+ch1) << endl;
    return 0;
}

　　2、3-2歌唱大赛选手成绩计算

#include <iostream>
using namespace std;
int main()
{
    int score, min = 100, max = 0, sum = 0;
    int n = 10;
    while(n--)
    {
        cin >> score;
        if(score<0 || score>100){
            cout << "the score is invalid." << endl;
            break;
        }
        if(score>max)
            max = score;
        if(score<min)
            min = score;
        sum += score;
    }
    if(n==-1)
        cout << (sum - max - min)/8.0 << endl;    
    return 0;
}

　　3、3-3猴子吃桃

#include <iostream>
using namespace std;
int main()
{
    int days,x=1;
    cin >> days;

    while(--days){
        x = 2*(x+1);
    }
    
    cout << x << endl;
    return 0;
}

　　4、3-4搬砖问题

#include <iostream>
using namespace std;
int main()
{
    int n, flag = 0;
    cin >> n;
    for(int men=0; men<=n/4; ++men)
    {
        for(int women=0; women<=(n-men)/3; ++women)
        {
            int children = n - men - women;
            //if(men*4*2+women*3*2+children==2*n){
            if(children%2==0 && men*4+women*3+children/2==n){
                cout << "men" << men << endl;
                cout << "women" << women << endl;
                cout << "children" << children << endl;
                flag = 1;
            }
        }
    }
    if(!flag)
        cout << "no result!" << endl;
    return 0;
}

　　5、3-5美分找钱

#include <iostream>
using namespace std;
int arr[] = {25, 10, 5};
int func(int left, int index)
{
    if(left==0 || index>=3)
        return 1;
    int count = 0;
    int x = left/arr[index];
    for (int i=x; i>=0; i--)
    {
        count += func(left - i*arr[index], index+1);
    }
    return count;
}
int main()
{
    unsigned int n, count = 0;
    cin >> n;
    if (n<0||n>99)
        cout << "the money is invalid!" << endl;
    else
        cout << func(n, 0) << endl;
    return 0;
}

#include <iostream>
using namespace std;
int MakeChangeCore(int n,int denom)
{
    int next_denom=0;
    switch(denom)
    {
    case 25:
        next_denom=10;
        break;
    case 10:
        next_denom=5;
        break;
    case 5:
        next_denom=1;
        break;
    case 1:
        return 1;
    }
 
    int res=0;
    for(int i=0;i*denom<=n;i++)
        res+=MakeChangeCore(n-i*denom,next_denom);
 
    return res;
}
 
int MakeChange(int n)
{
    if(n<=0)
            return -1;
    return MakeChangeCore(n,25);
}

int main()
{
    unsigned int n, count = 0;
    cin >> n;
    if (n<0||n>99)
        cout << "the money is invalid!" << endl;
    else
        cout << MakeChange(n) << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    unsigned int n, count = 0;
    cin >> n;
    if (n<0||n>99)
        cout << "the money is invalid!" << endl;
    else{
        for (int a=n/25; a>=0; a--)  //25美元
        {
            int ten = n-25*a;      //10美元
            for (int b=ten/10; b>=0; b--)
            {
                int five = ten - 10*b;   //5美元
                for (int c=five/5; c>=0; c--) 
                {   //(n-25*a-10*b-5*c) 1美元
                    /* if (25*a+10*b+5*c+(n-25*a-10*b-5*c) == n)
                    {
                        count++;
                    } */
                    count++;
                }
            }
        }
        cout << count << endl;
    }
    return 0;
}

　　第4周 基础练习

　　1、数组元素反序输出

#include <iostream>
using namespace std;
int main( )
{
    int n;
    cin >> n;
    int *arr = new int[n];
    for(int i=0; i<n; ++i)
        cin >> arr[i];
    cout << arr[n-1];
    for(int j=n-2; j>=0; --j)
        cout << " " << arr[j];
    return 0;
}

　　2、求数组元素最大值

#include <iostream>
#include <climits>
using namespace std;
int main( )
{
    int arr[100], index = 0; //其实数组无实质意义
    int max = INT_MIN;
    int x;
    for(; cin >> x, x != -9999; )
    {
        arr[index++] = x;
        if(arr[index-1] > max )
            max = arr[index-1];
    }
    cout << max << endl;
    return 0;
}

#include <iostream>
#include <climits>
using namespace std;
int main( )
{
    int max = INT_MIN;
    int x;
    for(; cin >> x, x != -9999; )
    {
        if(x > max )
            max = x;
    }
    cout << max << endl;
    return 0;
}

　　3、数组指定区间的元素的最大、最小、总和和平均值，总和及平均值均为double，总和若为整形，求平均值要强转

#include <iostream>
#include <climits>
using namespace std;
int main( )
{
    int arr[] = {-1,15,-40,-180,99,-122,-124,27,192,128,
                -165,95,161,-138, -183,51,107,39,-184,113,
                -63,9,107,188,-11,-13,151,-52,7,6};
    int i, j, max = INT_MIN, min = INT_MAX;     
    double sum = 0, ave = 0;
    cin >> i >> j;
    
    if(i<j && i>=0 && j<=30)
    {
        for(int k = i; k<j; ++k)
        {
            sum += arr[k];
            if(arr[k] > max) max = arr[k] ;
            if(arr[k] < min) min = arr[k];
        }    
        cout << max << " " << min << " " << sum << " " << sum/(j-i) << endl;    
    }    
    else cout << "0 0 0 0" << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main( )
{
    int arr[] = {-1,15,-40,-180,99,-122,-124,27,192,128,
                -165,95,161,-138, -183,51,107,39,-184,113,
                -63,9,107,188,-11,-13,151,-52,7,6};
    int i, j, max, min;     
    double sum = 0, ave = 0;
    cin >> i >> j;
    
    if(i<j && i>=0 && j<=30) // i,j条件
    {
        max = arr[i], min = arr[i]; //赋初始值
        for(int k = i; k<j; ++k)    //从i开始累加
        {
            sum += arr[k];
            if(arr[k] > max) max = arr[k] ;
            if(arr[k] < min) min = arr[k];
        }    
        cout << max << " " << min << " " << sum << " " << sum/(j-i) << endl;    
    }    
    else cout << "0 0 0 0" << endl;
    return 0;
}

　　4、求矩阵每行元素最大值

#include <iostream>
using namespace std;
int main( )
{
    //int arr[20][20]; //省略
    int row, col, x;
    cin >> row >> col;
    for( int i= 0; i<row; i++){
        cin >> x;
        int max = x;
        for(int j=1; j<col; ++j)
        {
            cin >> x;
            if(x>max) max = x;
        }
        cout << max << endl;
    }
    return 0;
}

#include <iostream>
using namespace std;
int main( )
{
    int arr[20][20]; 
    int row, col;
    cin >> row >> col;
    for( int i= 0; i<row; i++){
        cin >> arr[i][0];
        int max = arr[i][0];
        for(int j=1; j<col; ++j)
        {
            cin >> arr[i][j];
            if(arr[i][j]>max) max = arr[i][j];
        }
        cout << max << endl;
    }
    return 0;
}

　　5、求矩阵每列元素最大值，int max = arr[0][i];

#include <iostream>
using namespace std;
int main( )
{
    int arr[20][20]; 
    int row, col, i, j;
    cin >> row >> col;
    for( i= 0; i<row; i++){
        for( j=0; j<col; ++j)
        {
            cin >> arr[i][j];        
        }        
    }
    for( i= 0; i<col; i++){
        int max = arr[0][i];
        for(j=1; j<row; ++j)
        {
            if(max<arr[j][i])
                max = arr[j][i];
        }
        if(i) cout << " ";
        cout << max;
    }
    return 0;
}

　　6、计算向量的和

#include <iostream>
using namespace std;
int main( )
{
    int n;
    int arr1[100],arr2[100];
    cin >> n;
    for(int i=0; i<n; ++i)
        cin >> arr1[i];
    for(int i=0; i<n; ++i)
        cin >> arr2[i];
    for(int i=0; i<n; ++i){
        if(i) cout << " ";
        cout << arr1[i] + arr2[i];
    }    
    return 0;
}

　　7、矩阵向量的内积

#include <iostream>
using namespace std;
int main( )
{
    int n, sum = 0;
    int arr1[100],arr2[100];
    cin >> n;
    for(int i=0; i<n; ++i)
        cin >> arr1[i];
    for(int i=0; i<n; ++i)
        cin >> arr2[i];
    for(int i=0; i<n; ++i){
        sum += arr1[i] * arr2[i];
    }    
    cout << sum << endl;
    return 0;
}

　　8、计算向量的范数

#include <iostream>
#include <cmath>
using namespace std;
int main( )
{
    int n;
    double arr[100],sum = 0;
    cin >> n;
    for(int i=0; i<n; ++i){
        cin >> arr[i];
        sum += arr[i]*arr[i];
    }        
    cout << sqrt(sum) << endl;
    return 0;
}

#include <iostream>
#include <cmath>
using namespace std;
int main( )
{
    int n;
    double x, sum = 0;
    cin >> n;
    for(int i=0; i<n; ++i){
        cin >> x;
        sum += x * x;
    }        
    cout << sqrt(sum) << endl;
    return 0;
}

　　9、计算向量的欧氏距离，double类型

#include <iostream>
#include <cmath>
using namespace std;
int main( )
{
    int n;
    double sum = 0;
    double arr1[100],arr2[100];
    cin >> n;
    for(int i=0; i<n; ++i)
        cin >> arr1[i];
    for(int i=0; i<n; ++i)
        cin >> arr2[i];
    for(int i=0; i<n; ++i){
        sum += (arr1[i] - arr2[i]) * (arr1[i] - arr2[i]);
    }    
    cout << sqrt(sum) << endl;
    return 0;
}

　　10、矩阵求和

#include <iostream>
#include <cmath>
using namespace std;
int main( )
{
    int n, m;
    double arr1[100][100],arr2[100][100],sum[100][100];
    cin >> n >> m;
    for(int i=0; i<n; ++i)
    {
        for(int j=0; j<m; ++j)
            cin >> arr1[i][j];    
    }
    for(int i=0; i<n; ++i)
    {
        for(int j=0; j<m; ++j)
            cin >> arr2[i][j];
    }
    for(int i=0; i<n; ++i)
    {
        for(int j=0; j<m; ++j){
            sum[i][j] = arr1[i][j] + arr2[i][j];
            if(j) cout << " ";
            cout << sum[i][j];
        }
        cout << endl;
    }
    return 0;
}

#include <iostream>
using namespace std;
int main( )
{
    int n, m;
    double arr1[100][100], arr2[100][100];
    cin >> n >> m;
    for(int i=0; i<n; ++i)
    {
        for(int j=0; j<m; ++j)
            cin >> arr1[i][j];    
    }
    for(int i=0; i<n; ++i)
    {
        for(int j=0; j<m; ++j)
            cin >> arr2[i][j];
    }
    for(int i=0; i<n; ++i)
    {
        for(int j=0; j<m; ++j){            
            if(j) cout << " ";
            cout << arr1[i][j] + arr2[i][j];
        }
        cout << endl;
    }
    return 0;
}

　　11、输入字符串，求长度

#include <iostream>
using namespace std;
int main( )
{
    char str[100];
    cin.getline(str,100);
    char *p = str;
    int cnt = 0;
    while(*p)
    {
        cnt++;
        p++;
    }
    cout << cnt << endl;
    return 0;
}

　　12、统计字符串中大写字母的数量

#include <iostream>
using namespace std;
int main( )
{
    char str[100];
    cin.getline(str,100);
    char *p = str;
    int cnt = 0;
    while(*p)
    {
        if(*p>='A' && *p<='Z')
            cnt++;
        p++;
    }
    cout << cnt << endl;
    return 0;
}

　　13、复制字符串

#include <iostream>
using namespace std;
int main( )
{
    char s1[100], s2[100];
    cin >> s1;
    char* p1 = s1, *p2 = s2;
    while( *p2++ = *p1++ );
    cout << s2 << endl;
    return 0;
}

　　14、字符串逆序

#include <iostream>
using namespace std;
int main( )
{
    char s[100];
    cin >> s;
    
    int index = 0, i,j;
    while(s[index++]);
    
    for(i=0, j = index - 2; i<j; ++i,--j)
    {
        char t = s[i];
        s[i] = s[j];
        s[j] = t;
    }
    cout << s << endl;
    return 0;
}

　　15、定义表示平面坐标点的结构体计算两点距离

#include <iostream>
#include <cmath>
using namespace std;
struct POINT{
    double x, y;
};
int main( )
{
    POINT p1, p2;
    cin >> p1.x >> p1.y >> p2.x >> p2.y;
    cout << sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)) << endl;
    return 0;
}

　　第4周 中级练习

　　1、矩阵原地转置，for(j=0; j<i; ++j)

#include <iostream>
using namespace std;
int main( )
{
    int arr[10][10], i, j;
    int n;
    cin >> n;
    for(i=0; i<n; ++i){
        for(int j=0; j<n; ++j){
            cin >> arr[i][j];
        }
    }
    //转置
    for(i=0; i<n; ++i){
        for(j=0; j<i; ++j){
            if(i!=j){
                int t = arr[i][j];
                arr[i][j] = arr[j][i];
                arr[j][i] = t;
            }        
        }
    }
    for(i=0; i<n; ++i){
        for( j=0; j<n; ++j){
            if(j) cout << " ";
            cout << arr[i][j];            
        }
        cout << endl;
    }
    return 0;
}

　　2、判断对称矩阵，flag = 1;

#include <iostream>
using namespace std;
int main( )
{
    int arr[10][10], i, j;
    int n, flag = 0;
    cin >> n;
    for(i=0; i<n; ++i){
        for(j=0; j<n; ++j){
            cin >> arr[i][j];
        }
    }
    //判断对称
    for(i=0; i<n; ++i){
        for(j=0; j<i; ++j){
            if(arr[i][j] != arr[j][i]){
                flag = 1;
                break;
            }
        }
    }
    if(flag)
        cout << "No" << endl;
    else
        cout << "Yes" << endl;
    return 0;
}

　　3、去掉字符串末尾的空格

#include <iostream>
using namespace std;
int main( )
{
    char str[100];
    cin.get(str,100);
    cout << "|" << str << "|" << endl;
    
    char *p = str;
    while( *p ) p++;
    while( *--p == ' ' );
    *(p+1) = '';
    
    cout << "|" << str << "|" << endl;
    return 0;
}

　　4、去掉字符串开头的空格符

#include <iostream>
using namespace std;
int main( )
{
    char str[100];
    cin.get(str,100);
    cout << "|" << str << "|" << endl;
    
    char *p = str, *q = str;
    while( *p == ' ') p++;
    while( *q++ = *p++);
    
    cout << "|" << str << "|" << endl;
    return 0;
}

　　5、去掉字符串中间的所有空格，两头的空格保留，从后向前可能会覆盖（计算后头空格个数）

#include <iostream>
using namespace std;
int main( )
{
    char str[100];
    cin.get(str,100);
    cout << "|" << str << "|" << endl;
    
    //保留字符串前空格
    char *p = str, *q;
    while(*p == ' ') p++;
    q = p;
    
    //去掉字符串中间的空格
    while( *p )
    {
        if( *p != ' ' )
            *q++ = *p;        
        p++;
    }
    
    //计算字符串后的空格
    int cnt = 0;
    while(*--p == ' ')
        cnt++;
    while(cnt--)
        *q++ = ' ';
    *q = '';

    cout << "|" << str << "|" << endl;
    return 0;
}

　　6、查找子串

#include <iostream>
using namespace std;
int main( )
{
    char s1[100], s2[100];
    char *p, *q;
    gets(s1);
    gets(s2); 
    /*cin.getline(s1,100);
    cin.getline(s2,100);*/
    
    p = s1, q = s2; /* p,q 源串、目标串比较开始位置 */

    int cnt = 1;
    while(*p&&*q)
    {
        if (*p==*q)
        {
            p++;
            q++;
        }
        else
        {                  
            p = s1 + cnt++;
            q = s2;
        } 
    }
    if (*q=='') /* 匹配 */
        cout << cnt << endl;
    else
        cout << "没有该子串" << endl;
    return 0;
}

　　7、排序，插入排序

#include <iostream>
using namespace std;
int main( )
{
    int arr[100];
    int n, i, j;
    cin >> n;
    for(i=0; i<n; ++i)
        cin >> arr[i];
    for (j=1; j<n; j++ ) { 
        int t = arr[j];
        for ( i=j; i>0 && arr[i-1]<t; i-- )
            arr[i] = arr[i-1]; /*依次与已排序序列中元素比较并右移*/
        arr[i] = t; /* 放进合适的位置 */
    }
    for(i=0; i<n; ++i){
        if(i) cout << " ";
        cout << arr[i];
    }
    return 0;
}

　　8、二分查找，找到，break;

#include <iostream>
using namespace std;
int main( )
{
    int arr[300], index = 0;
    int x1, x2;
    
    for(; cin >> x1, x1 != -99999; )
        arr[index++] = x1;
    cin >> x2;
    
    int left = 0, right = index-1;
    while(left<=right)
    {
        int mid = (right-left)/2 + left; //防溢出
        if(arr[mid]>x2)
            right = mid - 1;
        else if(arr[mid]<x2)
            left = mid + 1;
        else{
            cout << mid << endl;
            break;
        }        
    }
    if(left>right)
        cout << -1 << endl;
    return 0;
}

　　第4周 编程作业

　　1、恺撒加密

#include <iostream>
using namespace std;
int main( )
{
    char str[256];
    cin >> str;
    char *p = str;
    while(*p)
    {
        char ch = 'a';
        char num = -32;
        if(*p>='A' && *p<='Z')
            ch = 'A', num = 32;
        *p = (*p - ch + 3)%26 + ch + num;
        p++;
    }
    cout << str << endl;
    return 0;
}

　　2、矩阵转置

#include <iostream>
using namespace std;
int main( )
{
    int n, arr[6][6]; 
    cin >> n;
    if(n<1 || n > 5)
        cout << "matrix order error" << endl;
    else{
        for(int i=0; i<n; ++i){
            for(int j=0; j<n; ++j){
                cin >> arr[j][i];
            }
        }
        for(int i=0; i<n; ++i){
            for(int j=0; j<n; ++j){
                if(j) cout << " ";
                cout << arr[i][j];
            }
            cout << endl;    
        }    
    }
    return 0;
}

　　3、按点击率显示歌曲

#include <iostream>
using namespace std;
struct SONG{
    char title[50];
    char name[20];
    int point;
};
int main( )
{
    SONG songs[5];
    int i, j;
    for(i=0; i<5; ++i){
        cin >> songs[i].title >> songs[i].name >> songs[i].point;
    }
    /* 插入排序 */
    for (j=1; j<5; j++ ) { 
        SONG t = songs[j]; /* 取出未排序序列中的第一个元素*/
        for ( i=j; i>0 && songs[i-1].point<t.point; i-- )
            songs[i] = songs[i-1]; /*依次与已排序序列中元素比较并右移*/
        songs[i] = t; /* 放进合适的位置 */
    }
    for(i=0; i<5; ++i){
        cout << songs[i].title << " " << songs[i].name << " ";
        cout << songs[i].point << endl;
    }     
    return 0;
}

　　4、星期转换

#include <iostream>
using namespace std;
int main( )
{
    const char *weeks[] = {"sunday","monday","tuesday","wednesday","thursday","friday","saturday"};
    int n;
    cin >> n;
    if(n<1||n>7)
        cout << "invalid" << endl;
    else
        cout << weeks[n%7] << endl;
    return 0;
}

　　5、插入加密，明文最后一个字符后也要打印插入字符

#include <iostream>
using namespace std;
int main( )
{
    char str[30], letter[6] = "abcde";
    int n, index = 0;
    
    cin >> str >> n;    
    char *p = str;
    
    while(*p){        
        int t = n;
        while(*p && t--){
            putchar(*p++);
        }    
        putchar(letter[index++]);
        index %= 5;
    }
    return 0;
}

#include <iostream>
using namespace std;
int main( )
{
    char str[30], letter[6] = "abcde";
    int n, index = 0;
    
    cin >> str >> n;    
    char *p = str;
         
    for(int t = n; *p; index %= 5){    //单循环            
        if(t--)
            putchar(*p++);
        //间隔后打印插入字符并恢复间隔, 明文最后一个字符后也要打印插入字符
        if(!*p || !t){  
            putchar(letter[index++]);
            t = n;
        }                    
    }
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    string s;
    string word[5] = {"a","b","c","d","e"};
    int step, index = 0;
    getline( cin, s );
    cin >> step;

    for(decltype(s.size())i=step; i<s.size(); i+=(step+1),index%=5){
        s.insert(i,word[index++]);
    }
    s += word[index];

    cout << s << endl;
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    string s;
    string word = "abcde";
    int step, n = 1, index = 0; //n插入的字符个数
    
    cin >> s >> step;

    for(int i=step; i<s.size(); i+=(n+step),index%=5){
        s.insert(i,n,word[index++]);
    }
    s.insert(s.size(),n,word[index]);//字符串尾部要求插入字符
    
    cout << s << endl;
    return 0;
}

　　6、三色球，枚举，j = i+1;

#include <iostream>
using namespace std;
int main( )
{
    enum color {red, yellow, blue};
    int tmp, i, j, t;
    for(i=red; i<=yellow; ++i){
        for(j=i+1; j<=blue; ++j){  //j=i+1
            for(t=0; t<2; ++t){    //二种选择或i或j
                switch(t){
                    case 0: tmp = i; break; //对应枚举
                    case 1: tmp = j; break;
                }
                switch((enum color)tmp){    //强转枚举
                    case red: cout << "red "; break;
                    case yellow: cout << "yellow "; break;
                    case blue: cout << "blue "; break;
                }                
            }
            cout << endl;
        }
    }
    return 0;
}

　　第5周 基础练习

　　1、求两个数的和

#include <iostream>
using namespace std;
double mysum(double a, double b){
    return a + b;
}
int main()
{
    double a, b;
    cin >> a >> b;   
    cout << mysum(a,b) << endl;
    return 0;
}

　　2、求绝对值的函数，double的最高位是符号位，位运算 &0x7fffffff 可以改变最高位的值

#include <iostream>
using namespace std;
double myfabs(double x){
    *((int*)&x + 1) &= 0x7fffffff;
    return x;
}
int main()
{
    double x;
    cin >> x;   
    cout << myfabs(x) << endl;
    return 0;
}

　　3、x的k次方

#include <iostream>
using namespace std;

double myfabs(double x){
    *((int*)&x + 1) &= 0x7fffffff;
    return x;
}

double mypow(double x, int n){
    double ret = 1;
    if( myfabs(x) <= 1e-7 )
        ret = 0.0;
    else if(!n) 
        ret = 1.0;
    else if( n<0 ){
        n = -n;
        for(int i=0; i<n; ++i)
            ret /= x;
    }
    else if(n>0){
        for(int i=0; i<n; ++i)
            ret *= x;
    }
    return ret;
}
int main()
{
    double x;
    int n;
    cin >> x >> n;   
    cout << mypow(x, n) << endl;
    return 0;
}

　　4、求n!的函数

#include <iostream>
using namespace std;

long fact(int n){
    long ret = 1;
    for(int i=1; i<=n; ++i)
        ret *= i;
    return ret;
}

int main()
{
    int n;
    cin >> n;   
    cout << fact( n ) << endl;
    return 0;
}

　　5、输入数组元素

#include <iostream>
using namespace std;

int input(int *arr){
    int index = 0, x;
    for(; cin >> x, x != -9999; )
        arr[index++] = x;
    return index;
}

int main()
{
    int arr[100];
    int n = input(arr);
    for(int i= n-1; i>=0; --i)
    {
        if(i != n-1)
            cout << " ";
        cout << arr[i];
    }
    return 0;
}

　　6、输出数组元素值

#include <iostream>
using namespace std;

int input(int *arr){
    int index = 0, x;
    for(; cin >> x, x != -9999; )
        arr[index++] = x;
    return index;
}

void output(int *arr, int n){
    for(int i= 0; i<n; ++i)
    {
        if(i)
            cout << " ";
        cout << arr[i];
    }
}

int main()
{
    int arr[100];
    int n = input(arr);
    output(arr, n);
    return 0;
}

　　7、将数组元素逆序

#include <iostream>
using namespace std;

int input(int *arr){
    int index = 0, x;
    for(; cin >> x, x != -9999; )
        arr[index++] = x;
    return index;
}

void output(int *arr, int n){
    for(int i= 0; i<n; ++i)
    {
        if(i)
            cout << " ";
        cout << arr[i];
    }
}

void reserve(int *arr, int n){
    for(int i=0, j=n-1; i<j; ++i, --j){
        int t = arr[i];
        arr[i] = arr[j];
        arr[j] = t;
    }
}

int main()
{
    int arr[100];
    int n = input(arr);
    reserve( arr, n);
    output(arr, n);
    return 0;
}

　　8、求数组元素的和

#include <iostream>
using namespace std;

int input(int *arr){
    int index = 0, x;
    for(; cin >> x, x != -9999; )
        arr[index++] = x;
    return index;
}

int addArr(int *arr, int n){
    int sum = 0; 
    for(int i=0; i<n; ++i)
        sum += arr[i];
    return sum;
}

int main()
{
    int arr[100];
    int n = input(arr);
    cout << addArr(arr, n) << endl;
    return 0;
}

　　9、求字符串的长度的函数

#include <iostream>
using namespace std;

int stringLength(char *p){
    int i = 0;
    while(p[i])
        i++;
    return i;
}

int main()
{
    char str[100];
    cin >> str;
    cout << stringLength(str) << endl;
    return 0;
}

　　10、字符串转大写

#include <iostream>
using namespace std;

void upper(char *p){    
    while(*p){
        if(*p>='a'&&*p<='z')
            *p -= 32;
        p++;
    }        
}

int main()
{
    char str[200];
    cin >> str;
    upper(str);
    cout << str << endl;
    return 0;
}

　　11、字符串复制函数

#include <iostream>
using namespace std;

void  mystrcpy(char s1[],char s2[]);

int main()
{
    char s1[100], s2[100];
    cin.getline(s1, 100);
    mystrcpy(s2,s1);
    cout << s2 << endl;
    return 0;
}

void  mystrcpy(char s1[],char s2[]){
    while(*s1++ = *s2++);
}

　　12、字符串比较函数

#include <iostream>
using namespace std;

int compare(char*, char*);

int main()
{
    char s1[200], s2[200];
    cin >> s1 >> s2;
    cout << compare(s1,s2) << endl;
    return 0;
}

int compare(char *s1, char *s2)
{
    int i, ret = 0;
    while( ! (ret = *( unsigned char *)s1 - *(unsigned char *)s2) && *s2)
        s1++, s2++;
    if ( ret < 0 )
        ret = -1 ;
    else if ( ret > 0 )
        ret = 1 ;
    return ret;    
}

　　第5周 中级练习

　　1、比较字符串（不区分大小写），比较不应修改字符串，可以用2个变量对两个字符串的字母取值，转为小写，比较

#include <iostream>
using namespace std;
int compare(const char*, const char*);
int main()
{
    char str1[100], str2[100];
    cin >> str1 >> str2;
    cout << compare(str1,str2) << endl;
    return 0;
}
int compare(const char *dst, const char *src)
{
    int ch1, ch2, ret = 0;
    do
    {
        if ( ((ch1 = (unsigned char)(*(dst++))) >= 'A') &&(ch1 <= 'Z') )
            ch1 += 0x20;
        if ( ((ch2 = (unsigned char)(*(src++))) >= 'A') &&(ch2 <= 'Z') )
            ch2 += 0x20;
    } while ( ch1 && (ch1 == ch2) );

    if ( ch1-ch2 < 0)
        ret = -1 ;
    else if ( ch1-ch2 > 0 )
        ret = 1 ;
    return ret;    
}

　　2、二分法解方程

#include <iostream>
#include <cmath>
using namespace std;
double fun(double x){
    return 2*x*x*x - 4*x*x + 3*x - 6;
}
int main()
{
    double left, right, middle, eps;
    cin >> left >> right >> eps;
    
    do
    {
        middle = (left+right)/2;
        if(fun(middle)*fun(left)>0)
          left = middle;
        else
          right = middle;
    }
    while(fabs(fun(middle))>=eps);
    
    cout << middle << endl;
    return 0;
}

　　3、牛顿法解方程，求导，3*a*x*x + 2*b*x + c

#include <iostream>
using namespace std;

double fun(double x){
    return x*x*x + 2*x*x + 3*x + 4;//系数a,b,c,d
}

double fun1(double x){
    return  3*x*x + 4*x + 3; //3*a*x*x + 2*b*x + c
}

double fabs(double x){
    *(((int *) &x) + 1) &= 0x7fffffff; //最高位, 置0
    return x;
}

int main()
{
    double x0, eps;
    cin >> x0 >> eps;

    while(fabs(fun(x0))>eps)
        x0 -= fun(x0)/fun1(x0);     

    cout << x0 << endl;    
    return 0;
}

　　4、输入、排序、查找

#include <iostream>
using namespace std;

int input(int *arr){ //输入
    int x, index = 0;
    for( ;cin >> x, x != -9999; )
        arr[index++] = x; 
    return index;
}

void insertSort(int *arr, int n){//插入排序
    int i, j, t;
    for (j=1; j<n; j++ ) { 
        t = arr[j];
        for ( i=j; i>0 && arr[i-1]>t; i-- )
            arr[i] = arr[i-1]; 
        arr[i] = t; 
    }
}

int findX(int *arr, int n, int x){//二分查找
    int left = 0, right = n-1, mid = -1;
    while(left<=right)
    {
        mid = (right-left)/2 + left; //防溢出
        if(arr[mid]>x)
            right = mid - 1;
        else if(arr[mid]<x)
            left = mid + 1;
        else
            break;
    }
    if(left>right) mid = -1;
    return mid;
}

void find5X(int *arr, int n){ //查找5个元素
    int x;
    for(int i=0; i<5; ++i)
    {
        cin >> x;
        cout << findX(arr, n, x) << endl;    
    }
}

int main()
{
    int arr[100], n;
    n = input( arr );
    insertSort( arr, n );
    find5X( arr, n );    
    return 0;
}

　　5、单词排序，用不到复制、大小写转换函数

#include <iostream>
using namespace std;

void insertSort(char **arr, int n);
int compare(const char *dst, const char *src);

int main()
{
    char **str = new char*[100];
    for(int i=0; i<100; ++i)
        str[i] = new char[20];
    int n;
    cin >> n;
    for(int i=0; i<n; ++i){
        cin >> str[i];
    }
    insertSort( str, n );
    for(int j=0; j<n; ++j)
        cout << str[j] << endl;
    return 0;
}

void insertSort(char **arr, int n){//插入排序
    int i, j, t;
    for (j=1; j<n; j++ ) { 
        char *t = arr[j];
        for ( i=j; i>0 && 1 == compare(arr[i-1],t); i-- )
            arr[i] = arr[i-1]; 
        arr[i] = t; 
    }
}

int compare(const char *dst, const char *src)
{
    int ch1, ch2, ret = 0;
    do
    {
        if ( ((ch1 = (unsigned char)(*(dst++))) >= 'A') &&(ch1 <= 'Z') )
            ch1 += 0x20;
        if ( ((ch2 = (unsigned char)(*(src++))) >= 'A') &&(ch2 <= 'Z') )
            ch2 += 0x20;
    } while ( ch1 && (ch1 == ch2) );

    if ( ch1-ch2 < 0)
        ret = -1 ;
    else if ( ch1-ch2 > 0 )
        ret = 1 ;
    return ret;    
}

　　6、识别数字，数字逐字累加后乘以符号存储数字；还可以数字累加后存储数字，符号也可以存储

#include <iostream>
using namespace std;

void solution(char *p)
{
    int i, arr[256], index = 0;
    int flag = 0, sum = 0, sign = 1; 
    
    for(i=0; p[i]; ++i)
    {
        if( p[i]>='0' && p[i]<='9' )
        {        
            sum = sum*10 + p[i] - '0';
            if( i && p[i-1] == '-' )
                sign = -1;
            flag = 1;
            continue;
        }    
        if(flag)
        {    
            arr[index++] = sum*sign;
            sign = 1; //符号置 1
            sum = 0;  //sum置 0
            flag = 0; //数字标记置 0
        }            
    }
    
    if(flag){ //字符串最后为数字
        arr[index++] = sum*sign;
    }
    
    for(i=0; i<index; ++i)
    {
        if(i) 
            cout << " ";
        cout << arr[i];    
    }
}

int main()
{
    char str[256];
    cin.getline(str,256);    
    solution(str);
    return 0;
}

#include <iostream>
using namespace std;

typedef struct {    
    short tag;//判断类型
    union {
        int num;
        char ch;
    }u; //联合体       
}SignedNumber;

void solution(char *p)
{
    SignedNumber arr[128]; //结构体数组
    int index = 0;
    int flag = 0, sum = 0; 
    
    for( ; *p; p++)
    {
        //与数字相关
        if( *p>='0' && *p<='9' )
        {        
            sum = sum*10 + *p - '0';    
            flag = 1;
            continue;
        }       
        if(flag)
        {    
            arr[index].u.num = sum;
            arr[index++].tag = 0;
            sum = 0; 
            flag = 0;
        }  
        //符号相关
        if(*p=='-' && *(p+1) && *(p+1)>='0'&&*(p+1)<='9'){
            arr[index].u.ch = *p;  
            arr[index++].tag = 1;
        }           
    }
    
    if(flag){ //字符串最后是数字
        arr[index].u.num = sum;
        arr[index++].tag = 0;
    }
    
    for(int i=0; i<index; ++i)
    {
        if(i && !arr[i-1].tag) //前面的元素是数字打印空格
            cout << " ";
        if(!arr[i].tag){
            cout << arr[i].u.num;
        }    
        else if(arr[i+1].u.num){//0前不打印符号
            cout << arr[i].u.ch;
        }        
    }
}

int main()
{
    char str[256];
    cin.getline(str,256);    
    solution(str);
    return 0;
}

　　第5周 编程作业

　　1、编写字符串反转函数mystrrev

#include <iostream>
using namespace std;

void mystrrev(char str[]);

int main()
{
    char s[100];
    cin.getline(s, 100);
    mystrrev(s);
    cout << s << endl;
    return 0;
}

void mystrrev(char str[]) 
{
    int i, j, len = 0;
    while(str[len]) len++;
    for(i=0, j=len-1; i<j; ++i, --j)
    {
        char t = str[i];
        str[i] = str[j];
        str[j] = t;
    }
}

　　2、编写一组求数组中最大最小元素的函数

#include <iostream>
using namespace std;

int imax(int array[], int count);
int imin(int array[], int count); 

int main()
{
    int arr[100];
    int n;
    cin >> n;
    for(int i=0; i<n; ++i)
        cin >> arr[i];
    cout << imax(arr, n) << endl;
    cout << imin(arr, n) << endl;
    return 0;
}

int imax(int array[], int count){
    int max = array[0];
    for(int i=1; i<count; ++i)
        if(max<array[i])
            max = array[i];
    return max;
}
int imin(int array[], int count){
    int min = array[0];
    for(int i=1; i<count; ++i)
        if(min>array[i])
            min = array[i];
    return min;
}

　　3、编写函数判断一个整数是否为素数，高效的算法是用一个数组存储素数，被素数整除的不是素数

#include <iostream>
using namespace std;

int isprime(int a);

int main()
{
    int a, flag = 0;
    for(; cin >> a, a; ){        
        if(isprime(a)){
            if(flag) cout << " ";
            cout << a;
            flag = 1;
        }
    }        
    return 0;
}

int isprime(int a){
    int ret = 1;
    if(a==1) ret = 0;
    for(int i=2; i<=a/i; ++i){
        if(a%i==0){
            ret = 0; 
            break;
        }
    }    
    return ret;
}

　　4、编写函数去除字符串中包含的非字母字符(不包括空格)，并将小写字母转换成大写字母

#include <iostream>
using namespace std;

void upperStr(char*);

int main()
{
    char str[200];
    cin.getline(str, 200);
    upperStr(str);
    cout << str << endl;
    return 0;
}

void upperStr(char* str){
    char *p = str;
    while(*p){
        if(*p>='a'&&*p<='z')
            *str++ = *p - 32;
        else if(*p>='A'&&*p<='Z'||*p == ' ')
            *str++ = *p;
        p++;
    }
    *str = *p;
}

　　5、编写函数计算一个英文句子中的单词个数，忽略非字母，发现字母计数，忽略字母，重复这个过程；一层循环，二个 if

#include <iostream>
using namespace std;

int countWords(char*);

int main()
{
    char str[500];
    cin.getline(str, 500);
    cout << countWords(str) << endl;
    return 0;
}

int countWords(char* p){
    int count = 0, flag = 1;//如果只一个字母
    for( ; *p; p++){
        if(!(*p>='a'&&*p<='z'||*p>='A'&&*p<='Z')){
            flag = 1; //之后是字母
            continue; //没有字母
        }
        if(flag){
            count++;
            flag = 0;
        }
    }
    return count;
}

　　第6周 基础练习

　　1、递归计算n!

#include <iostream>
using namespace std;

int fact( int n){
    if(n==1||n==0)
        return 1;
    return n*fact(n-1);
}

int main()
{
    int n; 
    cin >> n;
    cout << fact( n ) << endl;
    return 0;
}

　　2、递归计算1+2+3+…+n

#include <iostream>
using namespace std;

int sum( int n){
    if(n==0) //n 为 0 和为 0
        return 0;
    if(n==1)
        return 1;
    return n+sum(n-1);
}

int main()
{
    int n; 
    cin >> n;
    cout << sum( n ) << endl;
    return 0;
}

　　3、递归求数组元素的最大值

#include <iostream>
using namespace std;

int arrMax( int *arr, int n){
    int max;
    if(n==1)
        return arr[0];            
    max = arrMax(arr, n-1);
    if(arr[n-1]>max)
        max = arr[n-1];    
    return max;
}

int main()
{
    int n; 
    int arr[100];
    cin >> n;
    for(int i=0; i<n; ++i)
        cin >> arr[i];
    cout << arrMax( arr, n ) << endl;
    return 0;
}

　　4、递归求数组元素的和

#include <iostream>
using namespace std;

int arrSum( int *arr, int n){
    int sum;
    if(n==0)
        return 0; //n为0时返回0
    if(n==1)
        return arr[0];
    sum = arrSum(arr, n-1);
    sum += arr[n-1];
    return sum;
}

int main()
{
    int n; 
    int arr[100];
    cin >> n;
    for(int i=0; i<n; ++i)
        cin >> arr[i];
    cout << arrSum( arr, n ) << endl;
    return 0;
}

　　5、递归求Fibonacci序列的第n项

#include <iostream>
using namespace std;

int Fibonacci( int n){
    if(n==0)
        return 0;
    if(n==1)
        return 1;
    return Fibonacci(n-1) + Fibonacci(n-2);
}

int main()
{
    int n; 
    cin >> n;
    cout << Fibonacci( n ) << endl;
    return 0;
}

　　6、递归逆序数组元素

#include <iostream>
using namespace std;

void reverse(int *arr, int i, int j){
    if( i < j ){
        int t = arr[i];
        arr[i] = arr[j];
        arr[j] = t;
        reverse(arr, i+1, j-1);        
    }
}

int main()
{  
    int n;
    int arr[100];
    cin >> n;
    for(int i=0; i<n; ++i)
        cin >> arr[i];
    reverse(arr,0,n-1);
    for(int i=0; i<n; ++i){
        if(i) cout << " ";
        cout << arr[i];
    }
    cout << endl;    
    return 0;
}

　　7、输入输出数组元素的函数重载

#include <iostream>
#include <cmath>
using namespace std;

int input( int *ai );
int input( double *ad );
void print( int *ai, int ni );
void print( double *ad, int nd );

int main()
{  
    int ai[100];
    double ad[100];
    int ni, nd;
    ni = input( ai );
    nd = input( ad );
    print( ai, ni );
    print( ad, nd );
    return 0;
}

int input( int *ai ){
    int i = 0, x;
    for(; cin >> x, x != -9999;)
        ai[i++] = x;
    return i;
}
int input( double *ad ){
    int i = 0;
    double x;
    for(; cin >> x, fabs(x - (-9999))>1e-7; )
        ad[i++] = x;
    return i;
}
void print( int *ai, int ni ){
    for(int i=0; i<ni; ++i)
    {
        if(i) cout << " ";
        cout << ai[i];
    }
    cout << endl;
}
void print( double *ad, int nd ){
    for(int i=0; i<nd; ++i){
        if(i) cout << " ";
        cout << ad[i];
    }
    cout << endl;
}

　　8、逆序函数重载

#include <iostream>
#include <cmath>
using namespace std;

int input( int *ai );
int input( double *ad );
void print( int *ai, int ni );
void print( double *ad, int nd );
void reverse( int *ai, int ni );
void reverse( double *ad, int nd );

int main()
{  
    int ai[100];
    double ad[100];
    int ni, nd;
    ni = input( ai );
    nd = input( ad );
    reverse( ai, ni );
    reverse( ad, nd );
    print( ai, ni );
    print( ad, nd );
    return 0;
}

int input( int *ai ){
    int i = 0, x;
    for(; cin >> x, x != -9999;)
        ai[i++] = x;
    return i;
}
int input( double *ad ){
    int i = 0;
    double x;
    for(; cin >> x, fabs(x - (-9999))>1e-7; )
        ad[i++] = x;
    return i;
}
void print( int *ai, int ni ){
    for(int i=0; i<ni; ++i)
    {
        if(i) cout << " ";
        cout << ai[i];
    }
    cout << endl;
}
void print( double *ad, int nd ){
    for(int i=0; i<nd; ++i){
        if(i) cout << " ";
        cout << ad[i];
    }
    cout << endl;
}

void reverse( int *ai, int ni ){
    int i, j;
    for(i=0, j = ni-1; i<j; ++i, --j){
        int t = ai[i];
        ai[i] = ai[j];
        ai[j] = t;
    }
}
void reverse( double *ad, int nd ){
    int i, j;
    for(i=0, j = nd-1; i<j; ++i, --j){
        double t = ad[i];
        ad[i] = ad[j];
        ad[j] = t;
    }
}

　　9、数组元素求和函数的重载

#include <iostream>
#include <cmath>
using namespace std;

int input( int *ai );
int input( double *ad );
int mysum( int *ai, int ni );
double mysum(double *ad, int nd );

int main()
{  
    int ai[100];
    double ad[100];
    int sumi;
    double sumd;
    int ni, nd;
    ni = input( ai );
    nd = input( ad );
    sumi = mysum( ai, ni );
    sumd = mysum(ad, nd );
    cout << sumi << " " << sumd << endl;
    return 0;
}

int input( int *ai ){
    int i = 0, x;
    for(; cin >> x, x != -9999;)
        ai[i++] = x;
    return i;
}
int input( double *ad ){
    int i = 0;
    double x;
    for(; cin >> x, fabs(x - (-9999))>1e-7; )
        ad[i++] = x;
    return i;
}
int mysum( int *ai, int ni ){
    int sum = 0;
    for(int i=0; i<ni; ++i)
        sum += ai[i];
    return sum;
}
double mysum(double *ad, int nd ){
    double sum = 0.0;
    for(int i=0; i<nd; ++i)
        sum += ad[i];
    return sum;
}

　　10、交换两个元素值的重载函数

#include <iostream>
//#include <cstring>
using namespace std;

void swap( int &a, int &b);
void swap( double &a, double &b);
void swap ( int *a, int n, int *b, int m);
void swap ( char *a, char *b);
void print(int *arr, int n);

int main()
{
    int a, b;
    double da, db;
    int aa[100], ab[100];
    char s1[100], s2[100];
    int i, n, m;
    cin >> a >> b;
    cin >> da >> db;
    cin >> n;
    for(i=0; i<n; i++){
        cin >> aa[i];
    }
    cin >> m;
    for(i=0; i<m; i++){
        cin >> ab[i];
    }
    cin >> s1 >> s2;
    swap( a, b );
    swap( da, db );
    swap( aa, n, ab, m );
    swap( s1, s2);
    
    cout << a << " " << b << endl;
    cout << da << " " << db << endl;
    print( aa, m ); //交换
    print( ab, n );
    cout << s1 << " " << s2 << endl;
    return 0;
} 

void swap( int &a, int &b){
    int t = a;
    a = b;
    b = t;
}

void swap( double &a, double &b){
    double t = a;
    a = b;
    b = t;
}

void swap ( int *a, int n, int *b, int m){    
    int i;
    int count = n<m ? n : m;
    for(i=0; i<count; ++i){
        int t = a[i];
        a[i] = b[i];
        b[i] = t;
    }
    if(n<m){
        for(; i<m; ++i)
            a[i] = b[i];
    }
    if(n>m){
        for(; i<n; ++i)
            b[i] = a[i];
    }
}

void swap ( char *a, char *b){
    /* char *t = new char[100];
    strcpy( t, a );
    strcpy( a, b );
    strcpy( b, t );*/
    for(int i=0; a[i] || b[i]; ++i){
        char t = a[i];
        a[i] = b[i];
        b[i] = t;
    }
}

void print(int *arr, int n){
    for(int i=0; i<n; ++i){
        if(i) cout << " ";
        cout << arr[i];
    }
    cout << endl;
}

　　第6周 中级练习

　　1、递归插入排序

#include <iostream>
using namespace std;

int input(int *a);
void Insert( int *a, int n );  //插入
void InsertSort( int *a, int n ); //递归插入
void print(int *arr, int n);

int main()
{
    int data[100];
    int n;   
    n = input( data );
    InsertSort( data, n );
    print( data, n);
      
    return 0;
}

int input(int *a){
    int i = 0, x; // i = 0;
    for( ; cin >> x, x != -9999; )
        a[i++] = x;
    return i;
}

void print(int *arr, int n){
    for(int i=0; i<n; ++i){
        if(i) cout << " ";
        cout << arr[i];
    }
    cout << endl;
}

void Insert( int *a, int n )//把数组a的第n个数插入前n-1个数中
{
    int i = n-1;    //插入前n-1个元素中
    int key = a[n]; //保存插入元素
    while( (i>=0) && (key<a[i]) )
    {
        a[i+1] = a[i]; //前面元素后移
        i--;
    }
    a[i+1] = key; //找到位置
}

void InsertSort( int *a, int n )
{
    if( n>0 )
    {        
        InsertSort( a, n-1 ); // n 递减   
        Insert( a, n-1 );
    }
}

　　2、递归求两个数的最大公因数

#include <iostream>
using namespace std;

int gcd( int a, int b, int n ){
    if(n==1||a%n==0 && b%n==0)
        return n;        
    return gcd( a, b, n-1 );
}

int main()
{
    int a, b;
    cin >> a >> b;
    int n = a<b ? a : b;
    cout << gcd( a, b, n ) << endl;
    return 0;
}

　　3、全排列

#include <iostream>
using namespace std;

void print(int array[], int end);
void swap(int &a, int &b);
void permute(int array[], int begin, int end);

int main()
{
    int array[100];
    int n;
    cin >> n;
    for(int i=0; i<n; ++i)
        array[i] = i+1;
    permute( array, 0, n-1 );
    return 0;
}

void permute(int array[], int begin, int end)
{
    if (begin == end)
    {
        print(array, end);
    }
    else
    {
        for (int j = begin; j <= end; ++j)
        {
            swap(array[j], array[begin]);
            permute
            (array, begin+1, end); 
            swap(array[j], array[begin]); 
        }
    }
}

void print(int array[], int end)
{
    for (int i = 0; i <= end; ++i)
    {
       if(i) cout << " ";
       cout << array[i]; 
    }
    cout << endl;
}

void swap(int &a, int &b)
{
    int temp = a;
    a = b;
    b = temp;
}

　　4、递归构造可重复字符串

#include <iostream>
#include <cstring>
using namespace std;

void solution(int pos, char *p, int m, int n)
{
     if( pos == n ){
        cout << p << endl;
        return ;
     }
     for(int i='A'; i<'A'+m; i++)
     {
        p[pos] = i;
        solution( pos+1, p, m, n );
     }
}

int main()
{
     int m, n;
     cin >> m >> n;
     char *p = new char [n+1]; 
     p[n]='';
     solution( 0, p, m, n );
     delete []p;
     return 0;
}

　　5、自然数的拆分

#include <iostream>
using namespace std;

int n;
int a[10001] = {1};
int print( int );
int search( int s, int t );//回溯算法

int main()
{
   cin >> n;
   search( n, 1 );        //将要拆分的数n传递给s
   return 0;
}

int search(int s,int t)
{
    int i;
    for(i=a[t-1]; i<=s; i++)
        if(i<=n)                //当前数i要大于等于前1位数，且等于n
        {
            a[t] = i;            //保存当前拆分的数i
            s -= i;              //s减去i，s的值继续拆分
            if(s==0) print(t);  //s==0  拆分结束输出结果
            else search( s, t+1 ); //s>0，继续递归
            s += i;               //回溯：加上拆分的数，以便产分所有可能的拆分
        }
    return 0;
}

int print(int t)
{
   cout << n << "=";
   for(int i=1;i<=t;i++)
   {
        if(i==t)
        {
            cout << a[i];
            cout << endl;
        }
        else  cout << a[i] << "+";
   }
}

　　第6周 编程作业

　　1、递归猴子摘桃

#include <iostream>
using namespace std;

int   monkeyandPeak(int k,int n);

int main()
{
    int n = 10;
    cin >> n;
    int count = monkeyandPeak(1,n);
    cout << count << endl;

    return 0;
} 

int monkeyandPeak(int k,int n){
    if(n==1) return k;    
    /* k = monkeyandPeak(2*(k+1),n-1);
    return k; */
    return monkeyandPeak(2*(k+1),n-1);
}

　　2、编写内联函数求矩形的面积和周长

#include <iostream>
using namespace std;
inline void fun(int length, int width){
    cout << length*width << " " << 2*(length+width) << endl;
}
int main()
{
    int length, width;
    cin >> length >> width;
    fun(length, width);
    return 0;
}

　　3、编写重载函数显示字符串

#include <iostream>
#include <string>
#include <cstring>
using namespace std;

void print_spaced(char* str);
void print_spaced(string str);

int main()
{
    char str1[100];
    string str2;
    cin >> str1 >> str2;
    print_spaced( str1 );
    print_spaced( str2 );
    return 0;
}

void print_spaced(char* str){
    for(int i=0; i<strlen(str); ++i)
    {
        if(i) cout << " ";
        cout << str[i];
    }
    cout << endl;
}

void print_spaced(string str){
    for(int i=0; i<str.length(); ++i)
    {
        if(i) cout << " ";
        cout << str[i];
    }
    cout << endl;
}

　　4、排序函数重载

#include <iostream>
using namespace std;

void sort(int &a, int &b);
void sort(int &a, int &b, int &c);
void sort(int &a, int &b, int &c, int &d);

void Insert( int *a, int n );
void sort( int *a, int n );
void print(int *arr, int n);

int main()
{
    int a,b,c,d;
    int data[100];
    int k,n,i;

    cin >> k;
    
    switch(k)
    {
    case 1:
        cin >> a >> b;
        sort( a, b );
        cout <<a << " " << b <<endl;
        break;
    case 2:
        cin >> a >> b >> c;
        sort( a, b, c);
        cout << a << " " << b << " " << c << endl;          
        break;      
    case 3:
        cin >> a >> b >> c >> d;
        sort( a, b, c, d );
        cout << a << " " << b << " " << c << " " << d << endl;
        break;  
    case 4:
        cin >> n;
        for(i=0; i<n; i++)
        {
            cin >> data[i];
        } 
        sort( data, n );
        print( data, n);
        break;      
    }
    return 0;
}

void sort(int &a, int &b){
    if(a < b)
    {
        int t = a;
        a = b; 
        b = t;      
    }
}

void sort(int &a, int &b, int &c){
    sort(a,b);
    sort(a,c);
    sort(b,c);
}

void sort(int &a, int &b, int &c, int &d){
    sort(a,b,c);
    sort(a,d);
    sort(b,d);
    sort(c,d);
}

void print(int *arr, int n){
    for(int i=0; i<n; ++i){
        if(i) cout << " ";
        cout << arr[i];
    }
    cout << endl;
}

void Insert( int *a, int n )//把数组a的第n个数插入前n-1个数中
{
    int i = n-1;    //插入前n-1个元素中
    int key = a[n]; //保存插入元素
    while( (i>=0) && (key>a[i]) )
    {
        a[i+1] = a[i]; //前面元素后移
        i--;
    }
    a[i+1] = key; //找到位置
}

void sort( int *a, int n )
{
    if( n>0 )
    {        
        sort( a, n-1 ); // n 递减   
        Insert( a, n-1 );
    }
} 

　　5、编写递归函数来使字符串逆序

#include <iostream>
#include <cstring>
using namespace std;

void reverse(char *str, int i, int j){
    if( i < j ){
        char ch = str[i];
        str[i] = str[j];
        str[j] = ch;
        reverse(str, i+1, j-1);        
    }
}

int main()
{
    char str[100];
    cin.getline(str,100);  
    int len = strlen(str);
    reverse(str,0,len-1);
    cout << str;
    return 0;
}

　　第7周 基础练习

　　1、两个数的排序

#include <iostream>
using namespace std;

void sort(int *a, int *b){
    if( *a > *b ){
        int t = *a;
        *a = *b; 
        *b = t;
    }    
}

int main()
{
    int a, b;
    cin >> a >> b;
    sort( &a, &b );
    cout << a << " " << b << endl;
    return 0;
}

　　2、三个数的排序

#include <iostream>
using namespace std;

void sort(int *a, int *b);
void sort(int *a, int *b, int *c);

int main()
{
    int a, b, c;
    cin >> a >> b >> c;
    sort( &a, &b, &c );
    cout << a << " " << b << " " << c << endl;
    return 0;
}

void sort(int *a, int *b){
    if( *a > *b ){
        int t = *a;
        *a = *b; 
        *b = t;
    }    
}
void sort(int *a, int *b, int *c){
    sort(a,b);
    sort(a,c);
    sort(b,c);
}

　　3、返回数组的统计值（最大、最小、平均值、标准差）

#include <iostream>
#include <cmath>
using namespace std;

int input(double *a);
void statistics(double a[],int n,double *max,double *min,double *avg,double *stdev);

int main()
{
    double a[100];
    double max, min, avg, stdev;
    int n = input( a );
    statistics(a,n,&max,&min,&avg,&stdev);
    cout << max << " " << min << " " << avg << " " << stdev << endl;
    return 0;
}

int input(double *a){
    int n = 0;
    double x;
    for( ; cin >> x, fabs(x+9999)>1e-6; )
        a[n++] = x;
    return n;
}

void statistics(double a[],int n,double *max,double *min,double *avg,double *stdev){
    double sum1 = a[0], sum2 = 0.0;
    *max = *min = a[0];
    for(int i=1; i<n; ++i){
        if(a[i]>*max)
            *max = a[i];
        if(a[i]<*min)
            *min = a[i];
        sum1 += a[i];
    }
    *avg = sum1/n;
    for(int i=0; i<n; ++i){
        sum2 += (a[i]-*avg)*(a[i]-*avg);
    }
    *stdev = sqrt(1.0/n*sum2);
}

　　4、通过指向函数的指针调用函数

#include <iostream>
#include <cmath>
using namespace std;

double x2(double x);
double mysin(double x);

int main()
{
    double (*f)(double);
    double x;
    cin >> x;
    
    f = x2;
    cout << f(x) << " ";
    f = mysin;
    cout << f(x) << endl;
    
    return 0;
}

double x2(double x){     
    return x*x;
}

double mysin(double x){     
    return 2*sin(2*3.14*2*x+3.14);
}

　　5、计算任意一元函数值的通用函数

#include <iostream>
#include <cmath>
using namespace std;

double x2(double x);
double mysin(double x);
double  anyfun(double (*f)(double),double x);

int main()
{
    double x;
    cin >> x;
    cout << anyfun(x2,x) << " ";
    cout << anyfun(mysin,x) << endl;
    return 0;
}

double x2(double x){     
    return x*x;
}

double mysin(double x){     
    return 2*sin(2*3.14*2*x+3.14);
}

double  anyfun(double (*f)(double),double x){
    return f(x);
}

　　6、计算函数在指定区间的近似平均值

#include <iostream>
#include <cmath>
using namespace std;

double funavg(double (*f)(double x), double a,double b,int n);

int main()
{
    const int n = 1000;
    double a, b;
    cin >> a >> b;
    cout << funavg( exp, a, b, n ) << " ";
    cout << funavg( sin, a, b, n ) << " ";
    cout << funavg( cos, a, b, n ) << endl;
    return 0;
}

double funavg(double (*f)(double x), double a,double b,int n){
    double h = (b-a)/n, sum = f(a);
    double x = a;
    for(int i=1; fabs(b-x)>1e-6; ++i){
        x = a+i*h;
        sum += f(x);    
    }
    return sum/(n+1);
}

　　第7周 中级练习

　　1、指针实现向量的内积计算

#include <iostream>
#include <cmath>
using namespace std;

int input(double *a);
double solution(double *a, double *b, int n);

int main()
{
    double a[100], b[100];
    int n = input( a );
    input( b );
    cout << solution( a, b, n ) << endl;
    return 0;
}

int input(double *a){
    double *t = a, x;
    for( ; cin >> x, fabs(x+9999)>1e-6; )
        *a++ = x;
    return a - t;
}

double solution(double *a, double *b, int n){
    double sum = 0.0;
    for(int i=0; i<n; ++i)
        sum += (*a++) * (*b++);
    return sum;
}

　　2、使用指针的插入排序

#include <iostream>
using namespace std;

int input(int *a);
void InsertSort(int *arr, int n);

int main()
{
    int a[100];
    int n = input( a );
    InsertSort( a, n );
    for(int i=0; i<n; ++i){
        if(i) cout << " ";
        cout << *(a+i);
    }
    return 0;
}

int input(int *a){
    int *t = a, x;
    for( ; cin >> x, x != -9999; )
        *a++ = x;
    return a - t;
}

void InsertSort(int *arr, int n)
{
    int i;
    for(i=1; i<n; ++i){/*第0个元素有序，从第1个元素向右无序*/
        int j=i-1,key=*(arr+i);/*保存第i个元素，左边的元素i-1*/
        while(j>=0 && key<*(arr+j)){/*保存的元素key与之前的元素从右向左逐个比较*/
            *(arr+j+1)=*(arr+j);/*移动（向后赋值）*/
            j--;
        }
        *(arr+j+1)=key;/*j--退出，恢复正确值j+1*/
    }
}

　　3、指针实现成绩排序

#include <iostream>
using namespace std;

struct Student{
    int no;
    int achievement;
};

int input(Student *s);
void BubbleSort(Student *a,int left, int right);

int main()
{
    Student s[100];
    int n = input( s );
    BubbleSort( s, 0, n-1 );
    for(int i=0; i<n; ++i){
        cout << (s+i)->no << " " << (s+i)->achievement << endl;
    }
    return 0;
}

int input(Student *s){
    Student *t = s;
    int x, y;
    for( ; cin >> x >> y, x != 0; ){
        s->no = x;
        s->achievement = y;
        s++;
    }        
    return s - t;
}
/*冒泡排序--递归*/
void BubbleSort(Student *a,int left, int right)
{
    if(left<right){
        int j;
        Student t; 
        for(j=right; left<j; j--){
            if((a+j-1)->achievement>(a+j)->achievement)/*相邻比较*/ 
                t=*(a+j),*(a+j)=*(a+j-1),*(a+j-1)=t;  
        }
        BubbleSort(a,j+1,right);/*递归*/
    }
}

　　4、计算函数在某点的近似导数

#include <iostream>
#include <cmath>
using namespace std;
#define DELTA 0.001  //德尔塔

double solution(double (*fun)(double x), double x){     
    return ((*fun)(x+DELTA)-(*fun)(x-DELTA))/(2*DELTA); //导数公式
}
 
int main()
{
    double x;
    cin >> x;
    
    cout << solution(sin,x) << " ";
    cout << solution(cos,x) << " ";
    cout << solution(sin,x)+solution(cos,x) << endl;
    
    return 0;
}

　　5、计算函数在指定区间的近似积分

#include <iostream>
#include <cmath>
using namespace std;
#define N 100  // δ = (b-a)/n, n=100

double solution(double (*fun)(double x), double a, double b){ 
    double sum = 0.0;
    for(int i=0; i<N; ++i)
        sum += fun(a+i*(b-a)/N);
    return sum*(b-a)/N;
}
 
int main()
{
    double a, b;
    cin >> a >> b;
    
    cout << solution(sin,a,b) << " ";
    cout << solution(cos,a,b) << " ";
    cout << solution(sin,a,b)+solution(cos,a,b) << endl;
    
    return 0;
}

　　第7周 编程作业

　　1、编写函数重置两个变量的值

#include <iostream>
#include <cmath>
using namespace std;

void reset(int *a, int *b);

int main()
{
    int a, b;
    cin >> a >> b;
    reset( &a, &b );
    cout << a << " " << b << endl;
    return 0;
}

void reset(int *a, int *b){
    *a = (*a+*b)/2.0 + 0.5;
    *b = *a;
}

　　2、编写函数对数组中的元素求和

#include <iostream>
#include <cmath>
using namespace std;

int input( int *array);
void add_array(int a, int *sum);

int main()
{
    int array[100], sum = 0;
    int n = input( array );
    for(int i=0; i<n; ++i)
        add_array(array[i], &sum);
    cout << sum << endl;
    return 0;
}

int input( int *array){
    int x, i = 0;
    for( ; cin >> x, x != -1; )
        array[i++] = x; 
    return i;
}

void add_array(int a, int *sum){
    *sum += a;
}

　　3、数组清零

#include <iostream>
using namespace std;

int input( int *array);
void solution( int *array, int n);
void output(int *p, int count);

int main()
{
    int a[100], * p= a, n;
    int count = input( p );
    cin >> n;
    solution( p, n );
    output(p, count);
    return 0;
}

void solution( int *array, int n){
    for( int i=0; i<n; ++i )
        array[i] = 0;
}

int input( int *array){
    int x, i = 0;
    for( ; cin >> x, x != -1; )
        array[i++] = x; 
    return i;
}

void output(int *p, int count){
    for(int i=0; i<count; ++i)
    {
        if(i) cout << " ";
        cout << p[i];
    }
    cout << endl;
}

　　4、使用函数指针切换加密方法

#include <iostream>
using namespace std;

void caesar(char s[]);
void oddeven(char s[]);
void cipher(void (*f)(char s[]),char s[]);//形参为指向函数的指针，对应实参可为相应格式的函数名。

int main()
{
    char str[256];
    int n;
    cin >> str >> n;
    switch(n){
        case 1: cipher( caesar, str ); break;
        case 2: cipher( oddeven, str ); break;
    }
    return 0;
}

void caesar(char s[]){
    for(int i=0; s[i]; ++i)
    {        
        char ch = 'a';    
        if(s[i]>='a' && s[i]<='z'){
            s[i] -= 32; //转大写
            ch = 'A';
        }
        else{
            s[i] += 32; //转小写
        }
        s[i] = ( s[i] + 3 - ch ) % 26 + ch;
    }
    cout << s << endl;
}
void oddeven(char s[]){
    char str[256], index1 = 0, index2 = 0, i;
    for(i=0; s[i]; ++i){
        if(i%2) //下标为奇数的保存到str
            str[index1++] = s[i];
        else    //下标为偶数的保存到s
            s[index2++] = s[i];
    }
    for(i=0; i<index1; ++i)
        s[index2++] = str[i]; //把奇数的复制到s
    cout << s << endl;
}

void cipher(void (*f)(char s[]),char s[]){
    f(s);
}

　　5、编写求函数区间平均值的通用函数

#include <iostream>
using namespace std;

int a, b, c, m;
int  func1(int x);
int  func2(int x);
int avg( int (*f)(int),int x1,int x2);

int main()
{
    int x1, x2;
    cin >> a >> b >> c;
    cin >> m;
    cin >> x1 >> x2;
    cout << avg( func1, x1, x2 ) << endl;
    cout << avg( func2, x1, x2 ) << endl; 
    return 0;
}

int  func1(int x){
    return a*x*x+b*x+c;
}
int  func2(int x){
    int ret = 1;
    for(int i=0; i<m; ++i)
        ret *= x;
    return ret;
}

int avg( int (*f)(int),int x1,int x2){
    int sum = 0; 
    for(int i=x1; i<=x2; ++i){  //x1,x2 区间 
        sum += f(i);
    }
    return sum/(x2-x1+1);
}

　　第8周 基础练习

　　1、使用指针输出数组元素

#include <iostream>
using namespace std;
int main()
{
    const int N = 20;
    int *arr = new int[N]; //没有判断申请空间是否成功
    
    int *p = arr;
    int x, i = 0;
    for( ; cin >> x, x != 9999 && i<N ; i++ )
        *p++ = x;
    
    p = arr;
    
    /* for(int j=0; j<i; ++j)
    {
        if(j) cout << " "; //判断若干次
        cout << *p++;
    } 
    cout << endl;*/
    
    if(i) {  //判断一次
        cout << *p++;
        while(--i) 
            cout << " " << *p++;
        cout << endl;
    }
     return 0;
}

　　2、通过指针输入输出数组元素的函数

#include <iostream>
using namespace std;

int input(int *p);          //输入，返回输入的元素个数
void print(int *p,int n);   //显示数组元素，n为元素个数

int main()
{
    const int N = 100;
    int *arr = new int[N];
    
    int n = input( arr );
    print( arr, n );
    
     return 0;
}

int input(int *p){
    int x, i = 0; 
    for( ; cin >> x, x != 9999; ++i )
        *p++ = x;
    return i;
}

void print(int *p,int n){
    if(n) { 
        cout << *p++;
        while(--n) 
            cout << " " << *p++;
        cout << endl;
    }
}

　　3、指针实现字符串复制函数

#include <iostream>
using namespace std;

char * mystrcpy(char *s1,char *s2); //将s2中的内容复制到s1中，返回s1首地址

int main()
{
    char s1[100], s2[100];
    cin >> s2;
    cout << mystrcpy(s1,s2) << endl;
     return 0;
}

char * mystrcpy(char *s1,char *s2){
    char *s = s1;
    while( *s1++ = *s2++ );
    return s;
}

　　4、指针实现字符串比较，不区分大小写

#include <iostream>
using namespace std;

int mystrcmp(char *s1,char *s2);

int main()
{
    char s1[100], s2[100];
    cin >> s1 >> s2;
    cout << mystrcmp(s1,s2) << endl;
     return 0;
}

int mystrcmp(char *s1,char *s2)
{
    int ch1, ch2, ret = 0;
    do
    {
        if ( ((ch1 = (unsigned char)(*(s1++))) >= 'A') &&(ch1 <= 'Z') )
            ch1 += 0x20;
        if ( ((ch2 = (unsigned char)(*(s2++))) >= 'A') &&(ch2 <= 'Z') )
            ch2 += 0x20;
    } while ( ch1 && (ch1 == ch2) );

    if ( ch1-ch2 < 0)
        ret = -1 ;
    else if ( ch1-ch2 > 0 )
        ret = 1 ;
    return ret;    
}

　　5、通过指针访问结构体变量

#include <iostream>
using namespace std;
struct PERSON{
    char name[40], gender[10];
    int age;
};
int main()
{
    PERSON one;
    PERSON *p = &one;
    
    cin >> p->name >> p->gender >> p->age;
    
    cout << p->name << " " << p->gender << " " << p->age << endl;
    
     return 0;
}

　　6、通过指针访问结构体数组

#include <iostream>
#include <cstring>
using namespace std;
struct PERSON{
    char name[40], gender[10];
    int age;
};
int main()
{
    PERSON aclass[50];
    PERSON *p = aclass;
    int n = 0; //
    
    cin >> p->name >> p->gender >> p->age;
    while(strcmp(p->name,"0") && strcmp(p->gender,"0") && p->age)
    {
        n++;
        p++;
        cin >> p->name >> p->gender >> p->age;
    }
    
    p = aclass+n-1;
    while( p>=aclass ){
        cout << p->name << " " << p->gender << " " << p->age << endl;
        p--;
    }
    
     return 0;
}

　　7、动态申请变量，别忘了释放内存

#include <iostream>
using namespace std;
int main()
{
    int *a = new int;
    int *b = new int ;
    int *c = new int;
    
    cin >> *a >> *b >> *c;
    cout << (*a+*b+*c) << endl;
    delete a, b, c;
    
     return 0;
}

　　8、动态申请数组

#include <iostream>
using namespace std;
int main()
{
    double x, *p, *q;
    int n, k = 0;
    
    cin >> n;
    q = p = new double[n];
    
    for( ; cin >> x, x != 9999; k++)
        *q++ = x;
    
    q = p+k-1;
    cout << *q--;
    while( q>=p )
        cout << " " << *q--;
    cout << endl;
    delete []p;
    
     return 0;
}

　　9、动态申请结构体数组

#include <iostream>
#include <cstring>
using namespace std;
struct PERSON{
    char name[40], gender[10];
    int age;
};
int main()
{
    int i, n;
    PERSON *t, *p;
    cin >> n;
    t = p = new PERSON[n];
    
    cin >> t->name >> t->gender >> t->age;
    for( i=0; strcmp(t->name,"0") && strcmp(t->gender,"0") && t->age; ++i ){
        t++; //开始输入的不是 "0", t++ , 再次输入
        cin >> t->name >> t->gender >> t->age;
    }

    t = p+i-1;
    while( t>=p ){
        cout << t->name << " " << t->gender << " " << t->age << endl;
        t--;
    }
    
    delete []p;
     return 0;
}

　　10、动态申请结构体数组空间和结构体数组复制

#include <iostream>
#include <cstring>
using namespace std;
struct PERSON{
    char name[40], gender[10];
    int age;
};
int main()
{
    int i, n;
    PERSON *t, *p;
    cin >> n;
    t = p = new PERSON[n];
    
    cin >> t->name >> t->gender >> t->age;
    for( i=0; strcmp(t->name,"0") && strcmp(t->gender,"0") && t->age; ++i ){
        t++; //开始输入的不是 "0", t++ , 再次输入
        cin >> t->name >> t->gender >> t->age;
    }
    
    t = p+i-1;
    PERSON *t1, *p1;
    t1 = p1 = new PERSON[i];
    while(t>=p) *t1++ = *t--;
    
    t1 = p1;     //p1已经是逆序的
    while( t1<p1+i ){ //不越界, 小于p1+i
        cout << t1->name << " " << t1->gender << " " << t1->age << endl;
        t1++;
    }
    
    delete []p;
    delete []p1;
     return 0;
}

　　第8周 中级练习

　　1、IP地址转换1

#include <iostream>
using namespace std;

void InitBinStr(char *BinStr);
void NumToBinStr(char *BinStr, int n, int index);
void solution( const char *IpStr, char *BinStr );

int main()
{
    char IpStr[33],BinStr[33];
    cin >> IpStr;
    
    InitBinStr( BinStr );
    solution( IpStr, BinStr );
    
     return 0;
}

void InitBinStr(char *BinStr){ 
    char *p = BinStr; //为了更好理解 其实形参可以直接使用p
    for(int i=0; i<32; ++i) //赋值
        *p++ = '0';
    *p = '';  //保存二进制的字符数组，最后有个字符串结束符
}

void NumToBinStr(char *BinStr, int n, int index){
    while(n){
        BinStr[index--] = n%2 + '0';
        n /= 2;
    }
}

void solution( const char *IpStr, char *BinStr ){
    const char *p = IpStr; // 为了更容易书写
    for(int n=0,index=7; index<32; p++ )
    {    
        if(*p && *p != '.')//读数字
        {
            n = n*10 + *p - '0'; 
            continue;    
        }            
        NumToBinStr(BinStr,n,index);//遇到'.'或字符串读完 转换二进制
        index += 8;    //步长8
        n = 0;      //数字归零
    }
    cout << BinStr << endl;    
}

　　2、IP地址转换2

#include <iostream>
using namespace std;

int solution( const char * );

int main()
{
    char BinStr[33];
    cin >> BinStr;

    cout << solution( BinStr ); 
    for(int i=8; i<32; i+=8)
        cout << "." << solution( BinStr+i ); 
    
    return 0;
}

int solution( const char *p ){   
    int t = 8, n = 0;
    while(t--) 
        n += (*p++ - '0') << t;    
    return n;
}

#include <iostream>
using namespace std;

void solution( const char *BinStr );

int main()
{
    char BinStr[33];
    cin >> BinStr;

    solution( BinStr ); 

    return 0;
}

void solution( const char *BinStr ){
    const char *p = BinStr; // 为了更容易书写
    for(int n=0,t=8,cnt=0; cnt<4; p++ )
    {    
        if(t--)//读数字
        {
            n += (*p - '0') << t;
            continue;    
        }
        if(cnt) cout << ".";
        cout << n;
        cnt++;
        p--;    //t==0的时候p多++一次
        t = 8;
        n = 0;      //数字归零     
    }   
}

#include <iostream>
using namespace std;

void solution( char *IpStr, const char *BinStr );

int main()
{
    char IpStr[33],BinStr[33];
    cin >> BinStr;

    solution( IpStr, BinStr ); 

    return 0;
}

void NumToIpStr(char *IpStr,int n)
{
    static int index = 0;
    static int cnt = 0;
    
    if(n==0){
        IpStr[index++] = '0';
    }
      
    char tmp[3];
    int i = 0;
    while(n){        
        tmp[i++] = n%10 + '0';
        n /= 10;
    }
    
    while(i--)
        IpStr[index++] = tmp[i];
    
    if(++cnt<4){
        IpStr[index++] = '.';
    }
    else{
        IpStr[index] = '';
    }    
}

void solution( char *IpStr, const char *BinStr ){
    const char *p = BinStr; // 为了更容易书写
    for(int n=0,t=8,cnt=0; cnt<4; p++ )
    {    
        if(t--)//读数字
        {
            n += (*p - '0') << t;
            continue;    
        }
        NumToIpStr(IpStr,n);
        cnt++;
        p--;    //t==0的时候p多++一次
        t = 8;
        n = 0;      //数字归零     
    }   
    cout << IpStr << endl;    
}

　　3、找数据

#include <iostream>
using namespace std;

void solution(char *p)
{
    int i, index = 0;    
    int flag = 0, sum = 0, sign = 1;
    int dot = 0;
    
    for(i=0; ; ++i)
    {
        if( p[i]>='0' && p[i]<='9'|| p[i]=='.' )
        { 
            if( p[i] == '.' ){
                dot = 1;
                continue;
            }
            if(dot){ //记录小数点之后的位数
                dot *= 10;
            }
            sum = sum*10 + p[i] - '0';
            if( i && p[i-1] == '-' )
                sign = -1;
            flag = 1;
            continue;
        }    
        if(flag)
        {   
            if(dot){
                cout << 1.0*(sum*sign)/dot+9 << endl;
            }
            else{
                cout << sum*sign+9 << endl;
            }
            sign = 1; //符号置 1
            sum = 0;  //sum置 0
            flag = 0; //数字标记置 0
            dot = 0;
        }         
        if(!p[i]) 
            break;  //最后是数字可以输出
    }
}

int main()
{
    char str[256];
    cin.getline(str,256);    
    solution(str);
    return 0;
}

#include <iostream>
using namespace std;

struct IntAndDoubleArr{
    bool tag;
    union{
        double num1;
        int num2;
    }u;
};

void solution(char *p)
{
    IntAndDoubleArr arr[256];
    int i, index = 0;    
    int flag = 0, sum = 0, sign = 1;
    int dot = 0;
    
    for(i=0;  ; ++i)
    {
        if( p[i]>='0' && p[i]<='9'|| p[i]=='.' )
        { 
            if( p[i] == '.' ){
                dot = 1;
                continue;
            }
            if(dot){ //记录小数点之后的位数
                dot *= 10;
            }
            sum = sum*10 + p[i] - '0';
            if( i && p[i-1] == '-' )
                sign = -1;
            flag = 1;
            continue;
        }    
        if(flag)
        {   
            if(dot){
                arr[index].tag = true;
                arr[index++].u.num1 = 1.0*(sum*sign)/dot+9;
            }
            else{
                arr[index].tag = false;
                arr[index++].u.num2 = sum*sign+9;
            }    
            sign = 1; //符号置 1
            sum = 0;  //sum置 0
            flag = 0; //数字标记置 0
            dot = 0;
        }
        if(!p[i])
            break;            
    }
    
    for(i=0; i<index; ++i)
    {
        if(arr[i].tag)
            cout << arr[i].u.num1 << endl; 
        else
            cout << arr[i].u.num2 << endl;    
    }
}

int main()
{
    char str[256];
    cin.getline(str,256);    
    solution(str);
    return 0;
}

　　4、指针实现矩阵相加

#include <iostream>
using namespace std;

void solution( int *, int *, int, int );

int main()
{
    int i, j, k, index;
    cin >> i >> j;
    int *arr1 = new int[i*j];
    int *arr2 = new int[i*j];
    
    for( k=0,index=0; k<i*j; ++k )
        cin >> arr1[index++];
    for( k=0,index=0; k<i*j; ++k )
        cin >> arr2[index++];
    
    solution( arr1, arr2, i, j );
        
    return 0;
}

void solution( int *arr1, int *arr2, int i, int j)
{
    for( int k=0; k<i*j; ++k )
    {
        if( k && k%j==0 ) cout << endl;
        else if( k && k%j) cout << " ";
        cout << (*arr1++) + (*arr2++);
    }
    cout << endl;
}

　　5、指针实现矩阵相乘

#include <iostream>
using namespace std;

/*** 
    1、当矩阵A的列数（column）等于矩阵B的行数（row）时，A与B可以相乘;
    2、矩阵C的行数等于矩阵A的行数，C的列数等于B的列数;
    3、乘积C的第m行第n列的元素等于矩阵A的第m行的元素与矩阵B的第n列对应元素乘积之和; 
***/

void solution( int *, int *, int, int, int );

int main()
{
    int row1, column1, k, index;
    cin >> row1 >> column1;
    int *arr1 = new int[row1*column1];
    
    for( k=0,index=0; k<row1*column1; ++k )
        cin >> arr1[index++];
    
    int row2, column2;
    cin >> row2 >> column2;
    int *arr2 = new int[row2*column2];
    
    for( k=0,index=0; k<row2*column2; ++k )
        cin >> arr2[index++];
    
    //solution( arr1, arr2, row1, column1, row2, column2 ); //row2==column1
    solution( arr1, arr2, row1, column1, column2 );
        
    return 0;
}

void solution( int *arr1, int *arr2, int row1, int column1, int column2 )                               
{
    int *t1, *t2, k, row, column, sum = 0;  
    for( row=0; row<row1; row++ ) // row1
    {
        for( column=0; column<column2; column++ ) // column2
        {      
            t1 = arr1 + row * column1;
            t2 = arr2 + column;
            sum = 0;

            for( k=0; k<column1; k++ ) 
            {
                sum += (*t1) * (*t2); 
                t1 += 1;           //arr1数组的行
                t2 += column2;     //arr2数组的列 
            }
            
            if(column) cout << " ";
            cout << sum; 
        }
        cout << endl;
    }
}

　　第8周 编程作业

　　1、输出数字的英文名称

#include <iostream>
using namespace std;

const char * digitName(int n);

int main()
{
    int n;
    cin >> n;
    cout << digitName( n ) << endl;
        
    return 0;
}

const char * digitName(int n){
    const char *digitName[] = {"zero","one", "two", "three", "four", "five", "six", 
                               "seven", "eight", "nine", "ten", "eleven", "twelve"};
    return  digitName[n];
}

　　2、去除字符串首尾多余的空格

#include <iostream>
using namespace std;
int main( )
{
    char str[100];
    cin.get(str,100);
    
    char *p = str, *q = str;
    while( *p != '#' ) p++;
    while( *--p == ' ' );
    *(p+1) = '#';
    *(p+2) = '';
    
    p = str; 
    while( *p == ' ') p++;
    while( *q++ = *p++);
    
    cout << str << endl;
    return 0;
}

　　3、遍历二维数组

#include <iostream>
using namespace std;
int main()
{   
    int **a;  //指向指针的指针 
    int n, m;//n行 m列 
    int i, j;
    int sum = 0;
    cin >> n >> m; //输入行数和列数
 
    //申请空间
    a = new int * [n];  //n个 int 指针 数组
    for( i=0; i<n; i++ )    //n个大小为m的一维数组
    {
        a[i] = new int[m]; //1个大小为m的一维数组，a[i]是int指针
    } 
 
    //输入数据
    for( i=0; i<n; i++ )
    {
        for( j=0; j<m; j++ )
        {
            //cin>>a[i][j];//输入 
            cin>> *(*(a+i)+j);//同上a相当于行指针 
            sum += *(*(a+i)+j);
        }
    }
 
    cout << sum << endl;
    
    /*  //输出数据
    for(i=0; i<n; i++)
    {
        for(j=0; j<m; j++)
        {
            //cout<<a[i][j]<<"	";//输出 
            cout<< *(*(a+i)+j)<<"	";
        }
        cout<<endl;
    } */
    
    //释放申请的空间！！！
    for(i=0;i<n;i++) //释放n个大小为m的一维数组
    {
        delete []a[i]; 
    }
    delete []a;//释放int指针数组
    
    return 0;
}

　　4、动态申请大数组

#include <iostream>
using namespace std;

int *new_array(int n); 
void init_array(int *p, int n,int c); 

int main()
{   
    int n, c;
    cin >> n >> c;
    int *p = new_array( n );
    init_array( p, n, c);
    for( int i=0; i<n; ++i )
    {
        if(i) cout << " ";
        cout << *p;
    }
    delete []p;
    return 0;
}

int *new_array(int n){
    int *p = new int[n];
    return p;
}

void init_array(int *p, int n,int c){
    for( int i=0; i<n; ++i )
        *p++ = c;
}

　　5、矩阵对角线元素之和

#include <iostream>
using namespace std;
int main()
{   
    int n, sum = 0;
    cin >> n;
    int *p = new int[n*n];
    
    for( int i=0; i<n*n; ++i )
    {
        cin >> *p;
        if(i%(n+1)==0) sum += *p;
    }
    
    cout << sum << endl;
    delete []p;
    
    return 0;
}

　　6、十进制点分IP转换为32位二进制IP，IP合法性是没有连续的 '.'

#include <iostream>
using namespace std;

void InitBinStr(char *BinStr);
void NumToBinStr(char *BinStr, int n, int index);
void solution( const char *IpStr, char *BinStr );

int main()
{
    char IpStr[33],BinStr[33];
    cin >> IpStr;
    
    InitBinStr( BinStr );
    solution( IpStr, BinStr );
    
     return 0;
}

void InitBinStr(char *BinStr){ 
    char *p = BinStr; //为了更好理解 其实形参可以直接使用p
    for(int i=0; i<32; ++i) //赋值
        *p++ = '0';
    *p = '';  //保存二进制的字符数组，最后有个字符串结束符
}

void NumToBinStr(char *BinStr, int n, int index){
    while(n){
        BinStr[index--] = n%2 + '0';
        n /= 2;
    }
}

void solution( const char *IpStr, char *BinStr ){
    const char *p = IpStr; // 为了更容易书写
    //for(int n=0,index=7,flag=0; index<32; p++ )
    for(int n=0,index=7; index<32; p++ )
    {        
        if(*p>='0' && *p<='9') //是数字
        {
            n = n*10 + *p - '0'; 
            //flag = 1;
            continue;    
        }
        
        if(*(p+1)=='.'){ //经过测试题目要求的合法性是没有连续的'.'
            cout<<"data error"<<endl;  
            return;
        }
        //还有数字是否超过255 字符串是否超短 超长的情况
        /* if(*p && *p!='.' || !flag || *(p+1)=='.'){ //不是数字也不是 '.' 或第一个就是'.' 或连续的'.'
            cout<<"data error"<<endl;  
            return;
        }  */
        
        NumToBinStr(BinStr,n,index);//遇到'.'或字符串读完 转换二进制
        index += 8;    //步长8
        n = 0;      //数字归零
    }
    /* if(*(p-1)){  //字符串超长
        cout<<"data error"<<endl;  
        return;
    } */
    cout << BinStr << endl;    
}

#include <iostream>
using namespace std;

void InitBinStr(char *BinStr);
void NumToBinStr(char *BinStr, int n, int index);
void solution( const char *IpStr, char *BinStr );

int main()
{
    char IpStr[33],BinStr[33];
    cin >> IpStr;
    
    InitBinStr( BinStr );
    solution( IpStr, BinStr );
    
     return 0;
}

void InitBinStr(char *BinStr){ 
    char *p = BinStr; //为了更好理解 其实形参可以直接使用p
    for(int i=0; i<32; ++i) //赋值
        *p++ = '0';
    *p = '';  //保存二进制的字符数组，最后有个字符串结束符
}

void NumToBinStr(char *BinStr, int n, int index){
    while(n){
        BinStr[index--] = n%2 + '0';
        n /= 2;
    }
}

void solution( const char *IpStr, char *BinStr ){
    const char *p = IpStr; // 为了更容易书写
    for(int n=0,index=7; index<32; p++ )
    {        
        if(*p>='0' && *p<='9') //是数字
        {
            n = n*10 + *p - '0'; 
            continue;    
        }
        
        if(*(p+1)=='.'){ //经过测试题目要求的合法性是没有连续的'.'
            cout<<"data error"<<endl;  
            return;
        }
        
        NumToBinStr(BinStr,n,index);//遇到'.'或字符串读完 转换二进制
        index += 8;    //步长8
        n = 0;      //数字归零
    }
    cout << BinStr << endl;    
}