#define MATH_PI 3.14

void defineH() {
    // 宏在编译阶段就把宏对应的常量给替换了,所以很快；
    printf("%f", MATH_PI);
}

// 定义宏方法，宏方法没有具体的返回类型；当多行的时候，在后面添加一个反斜杠；
#define MAX(A,B) {\
     A>B?A:B \
}

    int a = 4;
    int *p;
    p = &a;
    printf("%d\n",p); // 地址值 
    printf("%d\n",*p); //数值>>4
    *p = 14;
    printf("%d\n",a); //数值发生改变>>14
    
    int arr[] = {1,2,3,4,5,6,7,8,9};
    p = arr; // p指向arr(实际上是指向了arr数组的第一个数值)
    printf("%d\n",*p); //>>1
    printf("%d\n",*(p+4)); // p+4，p往后移动>>4

    p = &arr[1];
    p = p+1;
    printf("%d\n",*p); //>>3

struct People {
    int age;
    char *name;
};

    struct People p;
    p.age = 12;
    printf("%d", p.age);

/**
 * 需要引入stdlib.h
 */
void structpointer() {
    // 声明一个People指针(需要初始化)并且分配一个内存地址，内存大小为结构体People的大小
    struct People *p = malloc(sizeof(struct People));
    p->age = 20;
    p->name = "ls";
    struct People *p1 = p;
    p1->name = "ls1";
    printf("hello struct People %s", p->name); // 输出结果为ls1
    // 使用malloc分配的指针在不需要使用之后需要释放
    free(p);
}

typedef struct  _Player
{
    int age;
    int job;
    union 
    {
        int classId;
        char officeAddress[20];
    }jobInfo;
}Player; 

/**
 * 函数指针
 */
void functionpointer(int i) {
    printf("hello functionpointer %d \n", i);
}
int functionpointer1() {
    printf("hello functionpointer1 \n");
    return 0;
}
void functionpointerexe() {
    void (*p)(int);
    p = functionpointer;
    p(34);
    int (*a)();
    a = functionpointer1;
    a();
}

typedef struct {
    int age;
} P1;

    P1 p;
    p.age = 12;
    printf("%d", p.age);

typedef int (*Void)();

Void v = functionpointer1;
v(); // 输出functionpointer1

// 如果没有定义HELLO_H_，则定义HELLO_H_，是为了防止头文件重复；
#ifndef HELLO_H_
#define HELLO_H_

void sayHello();

#endif /* HELLO_H_ */

#include <stdio.h>
// hello.h中sayHello具体实现
void sayHello() {
    printf("hello c");
}

#include "hello.h"

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

void fileRead1() {
    FILE * f = fopen("xx.txt", "r");
    fseek(f, 0, SEEK_END); // seek到文件末尾：获取文件大小
    long size = ftell(f); // 返回文件大小
    char buf[size + 1];
    fseek(f, 0, SEEK_SET); // 重新回到文件开始
    fread(buf, sizeof(unsigned char), size, f);
    buf[size] = '\0';
    fclose(f);
    printf("%s", buf);
}

void fileWrite1() {
    // f可能为空，需要进行判断！
    FILE * f = fopen("xx.txt", "w");
    fprintf(f, "hello c");
    fclose(f);
}

    srand((int) time(NULL ));
    int randNum = rand();
    printf("%d,", randNum);
    return 0;

    char buf[100];
    memset(buf, 0, 100); // 
    sprintf(buf, "hello c %d s%f,", 12, 23.2);
    printf("%s", buf);

void getput() {
    char buf[100];
    gets(buf); // 等待用户输入
    puts(buf);
}

int scanprint() {
    int a;
    scanf("%d", &a);
    printf("%d", a);
    return 0;
}