C / C++ / MFC

//WTF?
BigInt BigInt::add_bigint(BigInt add)
{
    int carry = 0;
    int temp;
    bool carry2;
    stack<int> answer;
    vector<int> tempvector;
    vector<int> add_int = add.get_bigint();
    
    while(bigint_int.size() > add_int.size())
         add_int.insert(add_int.begin(), 1, 0);

    while(bigint_int.size() < add_int.size())
         bigint_int.insert(bigint_int.begin(), 1, 0);
    cout<<add_int.size()<<" "<<bigint_int.size()<<"\n";
    for(int i = size(); i > 0 ;i--) //<------if I do size - 1 here
    {                                  //the first addition works but not the rest
        temp = add_int[i] + bigint_int[i];
        if(temp >= 10)
        {
            temp -= 10;
            carry2 = true;
        }
        else
            carry2 = false;

        answer.push(temp + carry);
        
        if(carry2)
            carry = 1;
        else
            carry = 0;
    }
    
    if(carry)
        answer.push(carry);
        
    while(!answer.empty())
    {
        tempvector.push_back(answer.top());
        answer.pop();
    }
    BigInt ret(tempvector);
    return ret;
}

int MakeBigger(int nVal1, int nVal2, int nMultiplier /*=2*/)
{
   int nRetValue;
   nRetValue = (nVal1+nVal2) * nMultiplier;
   return (nRetValue);
}

int MakeBigger(int nVal1, int nMultiplier/*=2*/, int nVal2)
{
}

int MakeBigger(int nMultiplier/*=2*/, int nVal1, int nVal2)
{
}

int MyFn(int nDefaultParam/*=2*/)

int MyFn(int nDefaultParam=2)