write your own strstr function.

1:  #include <stdio.h>  
2:  #include <string.h>  
3:  void *my_strstr(char *str1,char *str2)  
4:  {  
5:    int l1,l2;  
6:    l2 = strlen(str2);  
7:    if(!l2)  
8:      return (char *)str1;  
9:    l1 = strlen(str1);  
10:    while(l1>=l2)  
11:    {  
12:      l1--;  
13:      if ( !memcmp(str1,str2,l2))  
14:      {  
15:        return (char *)str1;  
16:      }  
17:      str1++;  
18:    }  
19:    return NULL;  
20:  }  
21:  main()  
22:  {  
23:    char str1[100] = "helloworld";  
24:    char str2[100] = "llo";  
25:    char *temp = my_strstr(str1,str2);  
26:    printf("%s\n",temp);  
27:    temp = strstr(str1,str2);  
28:    printf("%s\n",temp);  
29:  }