我分别建立了a.c ,b.c ,abc.h，放在同一目录了，在DEV C中建立了工程，一起放进去，但是无法编译啊。会显示why in the world are you trying to compile a empty project?...

源码：a.c:
#include <stdio.h>
#include <stdlib.h>
#include "abc.h"
int main (void)
{
    int a,b;
    puts("please input 2 numbers:");
    while (scanf("%d,%d",&a,&b)==2)
    printf("%d\n",plus(a,b));
    printf("%d",num);
    system("pause");
}

b.c:
#include "abc.h"
#include <stdio.h>
#include <stdlib.h>
int num=0;
int plus (int a,int b)
{
    num++;
    return (a+b);
}

abc.h:
//abc.h
int num;
int plus (int a,int b);