预编译宏定义

总结:

1.结构体指针如何人访问成员

2.结构体数组与指针如何访问某个元素的成员

3.条件编译如何进行条件编译

#import <Foundation/Foundation.h>

//预编译
//宏定义
#define PI 3.1415926//#define 的第一种形式
#define S(a,b) (a*b)//#define 的第二种形式
//注意:1推荐用大写 驼峰命名法 k+PI 或 PI
//    2宏不是变量
//pragma
#pragma mark add函数
void add (int a,int b){
}
#pragma mark sayHi函数
void sayHi(){
}
#pragma mark main 函数
//条件编译
//条件编译的第一种形式
#ifdef PI
int a = 10;
#else
int a = 20;
#endif
//条件编译的第二种形式
#ifndef wangnima
//没有定义宏定义过,执行代码段一
int b = 30;
#else
int b = 40;
#endif
//条件编译的第三种形式
#if 1
int c = 50;
#else
int c = 60;
#endif
int main(int argc, const char * argv[]) {
    printf("%d ",a);

    printf("%d ",b);

    printf("%d ",c);

    return 0;

}

#import <Foundation/Foundation.h>
typedef struct CPoint{
    float X;
    float y;
}CPoint;
typedef struct student{
    char name[20];
    char gender;
    float score;
}Student;

typedef struct person{
    char name[20];
    int age;
}person;
//打印person的name
void printName(person p){
    printf("%s ",p.name);
}
//打印数组的成员的name
void printArrName(person arr[],int n){//(person *arr[],int n)
    for (int i = 0; i < n; i++) {
        printf("%s ",(arr + i)->name);
    }
}
void scoreName(Student arr[],int n){
    Student *p = arr;
    for (int i = 0; i < n; i++) {
        if ((p+i)->gender == 'm') {
            (p+i)->score += 10;
            if ((p+i)->score > 100) {
                (p+i)->score = 100;
            }
        }
    }
    for (int i = 0; i < n; i++) {
        printf("%s %c % f ",(p+i)->name,(p+i)->gender,(p+i)->score);
    }
}
void ScoreName(Student *p,int n){
    for (int i = 0; i < n; i++) {
        if ((p+i)->gender == 'm') {
            (p+i)->score += 10;
            if ((p+i)->score > 100) {
                (p+i)->score = 100;
            }
        }
    }
    for (int i = 0; i < n; i++) {
        printf("%s %c % f ",(p+i)->name,(p+i)->gender,(p+i)->score);
    }

}

int main(int argc, const char * argv[]) {

 Student students[4] = {{"tangmaru",'m',91},{"wangnima",'m',96},{"ruhua",'f',80},{"zhangquandan",'m',90}};

 Student *ps = students;

for (int i = 0; i < 4; i++) {

if ((ps+i)->gender == 'm') {

(ps+i)->score += 10;

if ((ps+i)->score > 100) {

(ps+i)->score = 100;

} } }

for (int j = 0; j < 4; j++) {

printf("%s %c %.2f ",(ps+j)->name,(ps+j)->gender,(ps+j)->score);}

Student students[4] = {{"liubei",'m',98},{"zhangfei",'m',97},{"gaunyu",'m',98},{"zhaoyun",'m',99}};

    scoreName(students, 4);

    ScoreName(students, 4);

//    person p1 = {"wangnima",16};

//    person p2 = {"tangmaru",18};
//    person p3 = {"ruhua",20};
//    person arr[3] = {p1,p1,p3};
//    printArrName(arr,3);
//    printName(p1);
    //函数操作结构体数组时需要传入两个参数
    //1数组元素的首地址(结构体数组名)2结构体数组元素的个数

    //结构体指针 

//    CPoint arr = {10,20};
//    CPoint *p1= &arr;
//    p1 = &arr;
//   // arr.X 用点取出结构体变量的成员变量
//    printf("%.2f ",(*p1).X);

    //指针取结构体变量的成员变量 用*取值,然后再.

    //练习:定义一个学生的结构体,里面有两个成员变量 1 姓名 2 年龄 用指针打印成员变量
//    Student student = {"袁新峰",78};
//    Student student1 = {"刘振艺",18};
//    Student student2 = {"王明伟",17};
//    Student student3 = {"赵成浩",16};
//    Student *ps = &student,*ps1 = &student1,*ps2 = &student2,*ps3 = &student3;
//    ps = &student;
//    ps1 = &student1;
//    ps2 = &student2;
//    ps3 = &student3;
//    printf("%s %d ",(*ps).name,(*ps).age);
//    printf("%s %d ",(*ps1).name,(*ps1).age);
//    printf("%s %d ",(*ps2).name,(*ps2).age);
//    printf("%s %d ",(*ps3).name,(*ps3).age);
//    printf("%s %d ",ps->name,ps->age);
    //结构体指针访问成员变量,还可以用箭头这个符号
//    CPoint num1 = {10,30};
//    CPoint num2 = {10,5};
//    CPoint *pn1 = &num1;
//    CPoint *pn2 = &num2;
//    pn1 = &num1;
//    pn2 = &num2;
//    float num = 0;
//    num = sqrtf(((pn1->X-pn2->X)*(pn1->X-pn2->X))+((pn1->y-pn2->y)*(pn1->y-pn2->y)));
//    printf("%.2f ",num);
//    Student stu = {1, "lan ou",'m',89};
//    Student *ps = &stu;
//    ps = &stu;
////    ps->name[0] -= 32;
//      ps->name[0] ^= 32;//大小写互相转换用^=32
////    ps->name[0]= 'L';
////    char a1 = ps->name[0] - 32;
////    ps->name[0] = a1;
//    printf("%s ",ps->name);
//    //结构体数组数组名就是数组首元素的地址 也就是这个结构体数组的指针
//    Student students[5] = {{1, "lan ou",'m',89},{2, "lan ou",'m',89},{3, "lan ou",'m',89},{4, "lan ou",'m',89},{5, "lan ou",'m',89}};
//    Student *pst = students;

//    students[0]->number;

//    pst->number;

//    printf("%d ",pst->number);
//    printf("%d ",(pst+1)->number);
//    printf("%d ",(pst+2)->number);
//    printf("%d ",(pst+3)->number);
//    printf("%d ",(*(pst+4)).number);
//    printf("%d ",(*pst).number);
//    //*(p+i)等价于p[i]

//    for (int i = 0; i < 5; i++) {

//    printf("%d %s %c %f ",(pst+i)->number,(pst+i)->name,(pst+i)->gender,(pst+i)->score);

//    }
//    printf("%c ",pst->name[1]);
//    //结构体指针也是一个指针,他所占字节只与操作系统有关
//    //64位系统占8个字节 32位系统占4个字节

//    printf("%lu ",sizeof(pst));