C/string.h/strstr

    
//Declaration:  char *strstr(const char *str1, const char *str2); 
//Return:       It returns a null pointer if no match is found. 
  #include <string.h>
  #include <stdio.h>
  int main(void)
  {
    char *p;
    p = strstr("this is a test", "is");
    printf(p);
    return 0;
  }
         
/*
is is a test*/