sub in different bases

int subInBase(const int base, const int first, const int second) {
    if (base < 1 || base > 10) {
        puts("bad base");
        return INT_MAX;
    }
    char sgn = 1;
    int cp_first, cp_second;
    int result = 0;
    if (first >= second) {
        cp_first = first;
        cp_second = second;
    } else {
        cp_first = second;
        cp_second = first;
        sgn = -1;
    }
    int carry = 0;
    int k = 1;
    while (cp_first > 0) {
        int sub = cp_first % 10 - cp_second % 10;
        if (sub < 0) {
            result += (sub + base) * k;
            carry = 1;
        } else {
            result += sub * k;
            carry = 0;
        }
        k *= 10;
        cp_first /= 10;
        cp_first -= carry;
        cp_second /= 10;
    }
    return result * sgn;
}