How can i use unsigned short int and short int to subtract hugeinteger in C++?

I try my best to code something in C++.When i use unsigned int and int to subtract, that's OK. However, using the unsigned short int and short int to subtract, i have a problem. So what i need to do in my code?

Thanks a lot.

Test value:

21758612232416725117133766166700 1758612232416725117155428849047

In the beginning, i have to define

*this > op2

absolutely.

template< typename T >
HugeInteger< T > HugeInteger< T >::operator-(const HugeInteger &op2)const // subtraction operator; HugeInteger - HugeInteger
{
    int size = integer.getSize();
    int op2Size = op2.integer.getSize();
    int differenceSize = size;
    HugeInteger < T > difference(differenceSize);

    difference = *this;

    Vector<T>::iterator it = difference.integer.begin();

    int counter = 0;

    for (Vector<T>::iterator i = difference.integer.begin(), j = op2.integer.begin(); j < op2.integer.end(); i++, j++) {
        if ((*i - *j - counter) < 10) {
            *i -= (*j + counter);
            counter = 0;
        }
        else {
            *i += 10;
            *i -= (*j + counter);
            counter = 1;
        }
    }

    while (counter == 1) {
        if ((*(it + op2Size) - counter) < 10) {
            *(it + op2Size) -= counter;
            counter = 0;
            op2Size++;
        }

        else {
            *(it + op2Size) += 10;
            *(it + op2Size) -= counter;
            counter = 1;
            op2Size++;
        }
    }

    if (*this == op2) {
        HugeInteger<T> zero(1);
        return zero;
    }

    for (Vector<T>::iterator i = difference.integer.end() - 1; i > difference.integer.begin(); i--) {
        if (*i == 0) {
            differenceSize--;
        }

        else {
            break;
        }
    }

    difference.integer.resize(differenceSize);
    return difference;
}