int strcmp(const char *s1, const char *s2)
{
    int i;
    for (i = 0; s1[i] == s2[i]; i++)
        if (s1[i] == '\0')
            return 0;

    return s1[i] - s2[i];
}

int strncmp(const char *s1, const char *s2, unsigned long n)
{
    for (; n > 0; s1++, s2++, --n)
        if (*s1 != *s2)
            return ((*(unsigned char *)s1 < *(unsigned char *)s2) ? -1 : 1);
        else if (*s1 == '\0')
            return 0;
    return 0;
}