STRSTR Implementation in C

const char * strstr ( const char * str1, const char * str2 );
      char * strstr (       char * str1, const char * str2 );

Returns a pointer to the first occurrence of str2 in str1, or a 
null pointer if str2 is not part of str1.

The matching process does not include the terminating 
null-characters, but it stops there.

#include 
char *mystrstr(const char *str1, const char *str2){
    char *a, *b;
    while(*str1){
        a = str1;
        b = str2;
        while(*a && *b && (*a == *b)) a++, b++;
        if(*b == '\0') return a;
        str1++;
    }
    return NULL;
}

int main(){
    char *a = "Andaman and Nicobar is a beautiful island";
    char *b = "and ";
    char *res = mystrstr(a,b);
    if(res)
        printf("%s\n", res);
    else
        printf("Substring not found\n");
    return 0;
}

//Output: Nicobar is a beautiful island