C skills : tutor 5: StrStr Library function

char *strstr(char *string1, char *string2); 

Description:

The strstr function locates the first occurrence of the string string2 in the string string1 and returns a pointer to the beginning of the first occurrence.

Return Value

The strstr function returns a pointer within string1 that points to a string identical to string2. If no such sub string exists in src a null pointer is returned.

/* user defined strstr */

#include "stdio.h"


char * strstr_ud(char *, char *);

int main()
{

char s1 [] = "This House is Nice";
char s2 [] = "My Car is White";

printf("Returned String 1: %s\n", strstr_ud(s1, "House"));
printf("Returned String 2: %s\n", strstr_ud(s2, "Car"));
return 0;

}

char * strstr_ud(char * str1, char * str2)
{
   char *temp1=NULL;
    char *temp2=NULL;
    temp2 = str2;
    while(*str1++ != '\0')
    {
       if(*str2 == *str1)
       {
           temp1 = str1;
           while(*str2 != '\0')
           {
               if(*str2 != *temp1)
               {
                   flag = 1;
               }
               else
               {
                   flag = 0;
               }
               str2++;temp1++;
           }
           if(flag == 0)
           {
               return str1;
           }
           else
           {
             str2 = temp2;
           }
       }
    }
    return NULL;}


Output
House is Nice
Car is White