C语言多文件编译

fun.c

#include <stdio.h>
int fun1(){
    printf("The first function!\n");
    return 0;
}
int fun2(){
    printf("The second function!\n");
    return 0;
}
int fun3(){
    printf("The third function!\n");
    return 0;
}

fun.h

#ifndef _FUN_H
#define _FUN_H

extern int fun1(void);
extern int fun2(void);
extern int fun3(void);

#endif

main.c

#include <stdio.h>
#include <stdlib.h>
#include "fun.h"

int main(){
    fun1();
    fun2();
    fun3();

    system("pause");
    return 0;
}

对上面的每个 .c 文件都进行编译，然后链接并运行：
The first function!
The second function!
The
third function!