#include <string.h>
int  main(void){
char *s1 = "hello";
char *s2 = "hello world";
char *s3 = "goodnight vienna";
char *res;
res = strstr(s1, s2);
sprintf("result %s\n", res);
res = strstr(s1, s3);
sprintf("result %s\n", res);
}

Segmentation fault