char* MyStrstr(char* pszSearchString, char* pszSearchWord);
int main(int argc, char* argv[])
{
    char szTemp1[20] = {0};
    char szTemp2[10] = {0};
    char * pszTemp1 = NULL;
    strcpy(szTemp1, "aabaaacaamaad");
    strcpy(szTemp2, "aa");

    pszTemp1 = MyStrstr(szTemp1, szTemp2);
    printf("%s", pszTemp1);
    getch();
    return 0;
}

char* MyStrstr(char* pszSearchString, char* pszSearchWord)
{
    int nFcount = 0;
    int nScount = 0;
    int nSearchLen = 0;
    int nIndex = 0;
    char* pszDelString = NULL;

    if(pszSearchString == NULL || pszSearchWord == NULL) {
    return NULL;
    }

    while(pszSearchWord[nSearchLen] != '') {
        nSearchLen++;
    }
    if(nSearchLen <= 0){
        return pszSearchString;
    }

    for(nFcount = 0; pszSearchString[nFcount] != ''; nFcount++) {
        if(pszSearchString[nFcount] == pszSearchWord[nScount]) {
           nScount++;
        } else {
           nScount = 0;
        }

        if(nScount == nSearchLen) {
            nIndex = (nFcount - nScount) + 1;
            pszDelString = pszSearchString + nIndex;
            return pszDelString;
        }
   }
   return NULL;
}

char * strstr(const char *in, const char *str)
{
    char c;
    size_t len;

    c = *str++;
    if (!c)
        return (char *) in; // Trivial empty string case

    len = strlen(str);
    do {
        char sc;

        do {
            sc = *in++;
            if (!sc)
                return (char *) 0;
        } while (sc != c);
    } while (strncmp(in, str, len) != 0);

    return (char *) (in - 1);
}