求助为什么没有输出结果，求佬教教，我已经卡好几天了

#include <stdio.h>#include <string.h>char* strin(char* a, char* b){char* p = a, * t;while (1){t = b;while (*p != *t && *p != '\0')p++;if (*p == '\0')return NULL;while (*p == *t && *t != '\0') { t++; p++; };if (t == '\0')return a;}}int main(void){char* ptr = strin("hat", "at");if(ptr!=NULL)puts(ptr);return 0;}