strstr - Returns a pointer to the first occurrence of str2 in str1 or a null pointer if there str2 is not part of str1 in C

//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");

    return 0;

is a test