C语言之子串查询字符串函数

#include<stdio.h>
#include<assert.h>
char *strstrr(const char*strSrc, const char *str)
{
    const char *s = strSrc; 
    const char *t = str;
    assert((strSrc != NULL) && (str != NULL));
    for(; *s != '\0'; ++strSrc)
    {
        for(s = strSrc,t = str; *t != '\0' && *s == *t; ++s, ++t)
            NULL;
        if(*t == '\0')
            return (char*)strSrc;
    }
    return NULL;
    
}
int main()
{
char a[] = "i have a apple!";
char b[] = "applh";
char *c = strstrr(a, b);
if(c == NULL)
printf("NO");
else
printf("%d",c); 
}