例：输入abcdabfg 输入ab 输出abfg

#include<stdio.h>char *fun(char *a,char *b){char *t,*r,*s;s="NULL";while(*a!='\0'){t=a;r=b;while(r!='\0')if(*t==*r){t++;r++;}elsebreak;if(*r=='\0')s=a;a++;}return s;}int main(){char a[100],b[100];char *p;printf("enter string:");gets(a);printf("enter substring:");gets(b);p=fun(a,b);printf("the result is:%s",p);return 0;}