编译以下程序，你将得到编译器的警告

/* test.c */

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

int main(void)
{
        int i = 5;
        int* ptr = malloc(1);
        char ch = 'e';
        /* Checking an int vs the other two */
        if ( i == NULL)
                puts ("This shouldn't happen");
        else
                puts ("But this should");
        if ( i == '\0')
                puts ("This shouldn't happen");
        else
                puts ("But this should");
        /* Checking a ptr vs the other two */
        if ( ptr == 0)
                puts ("This shouldn't happen");
        else
                puts ("But this should");
        if ( ptr == '\0')
                puts ("This shouldn't happen");
        else
                puts ("But this should");
        /* Checking a character vs the other two */
        if ( ch == NULL)
                puts ("This shouldn't happen");
        else
                puts ("But this should");
        if ( ch == 0)
                puts ("This shouldn't happen");
        else
                puts ("But this should");
        free(ptr);
        
        getchar();
        return 0;
}

==========================================
test.c: In function `main':
test.c:10: warning: comparison between pointer and integer
test.c:28: warning: comparison between pointer and integer

我用的是 Dev-C++
可以在这里下载 http://free3.e-168.cn/antigloss/blog.php?do_showone/tid_42.html

此外，大家也可以参考这个网站 http://www.eskimo.com/~scs/C-faq/s5.html