gcc demo.c? max.c?

demo.c: In function ‘main’:

demo.c:7:18: warning: implicit declaration of function ‘max’; did you mean ‘main’? [-Wimplicit-function-declaration]

? ? ?int maxNum = max(a1,a2);

? ? ? ? ? ? ? ? ? ^~~

? ? ? ? ? ? ? ? ? main

代碼如下：

#include <stdio.h>

// #include "max.c"

int main()

{

? ? int a1 = 30;

? ? int a2 = 32;

? ? int maxNum = max(a1,a2);

? ? printf("the max value is %d\n",maxNum);

? ? return 0;

}