C++ 考级试题

1. 输出保留指定小数的浮点数: cout.precision()

#include "iostream"
using namespace std;
int main()
{
    double num;
    cin >> num;
    
    //
    cout.precision(12);
    cout << fixed << num;
    
    return 0;
}

2. 设置输出数据的宽度:  cout.width()

#include <iostream>
using namespace std;

int main()
{
    for (int i = 0; i < 100; i++) {
        cout.width(3);                                  // 仅对下一个cout输出生效
        cout << i << endl;
    }
}

3. 计算经过多少天之后是星期几

// base:    当前是星期几
// passed:  过了多少天
int week(int base, int passed)
{
    int week = (base+passed) % 7;
    int week_a[7] = {7,1,2,3,4,5,6};
    return week_a[week];
}

4. Hello, World!的大小（sizeof）

#include <iostream>
using namespace std;

int main(void)
{
    int n;
    string hello = "Hello, World!";
    
    n = sizeof(hello);
    cout << n << endl;
    return 0;
}

 5. 创建素数表的函数

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

int creat_prime(int n, int prime[])
{
    prime[0] = 0;
    prime[1] = 0;
    // 素数标志
    for (int i=2; i<n; i++) {
        prime[i] = 1;
    }
    // 遍历到根号n
    for (int i=2; (i*i)<n; i++) {
        if (prime[i] == 1) {
            for (int j=2*i; j<=n; j++) {
                if ((j%i) == 0) {
                    prime[j] = 0;
                }
            }
        }
    }
    return 0;
}

int main(void)
{
    int n;
    cin >> n;
    //
    int *prime = new int[n];
    creat_prime(n, prime);
    for (int i=0; i<n; i++) {
        if (prime[i] != 0) {
            cout << i << endl;
        }
    }
    return 0;
}

 6. 辗转法求最大公约数

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

int gcd(int m, int n)
{
    int r = m % n;
    if (r == 0) {
        return n;
    }
    else {
        return gcd(n, r);
    }
}

int main()
{
    int a, b;
    cin >> a >> b;
    cout << gcd(a, b);
}