Newbie questions about bloated binary to decimal converter

[getajob92]

Hi all, I'm new to programming and I'm having some minor difficulties with a console app I've made to convert a given binary number into decimal. This program is probably ugly and ultra bloated, so I would gladly accept advice on that front, but keep in mind that we're only using pretty basic stuff. We're not even allowed to use strings.

Basically I have 2 questions.
1. Because of how limited integers are in terms of storage, the largest binary number i can give seems to be 1 111 111 111. Anything larger breaks the program. Is there any way to increase the largest input I can give without completely rewriting the program? I tried changing the num/numCounter (and the typecasting) to long doubles in a blind hope that that would, help, but it just messed stuff up (or I did).

2. I'd also like to make it so that if someone inputs a non-binary number my program tells them so and stops. I figured a switch statement within the while loop would work (for when numCounter/divisor is negative or greater than 1), but I was wondering if instead it was possible to use an if statement that could break the while loop? Any other suggestions?

Anyway, here's the code:

#include <QtCore/QCoreApplication>
#include <iostream>
#include <cstdlib>
#include <iomanip>
#include <cmath>


using namespace std;

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    char again;
    cout<<"This program will convert a binary number into decimal form."<<endl<<endl;
    do
    {
        int numDigits, divisor, ans=0;
        int num, numCounter;
        cout<<"Please enter the binary number."<<endl;
        cin>>num;
        numCounter = num;
        numDigits = static_cast<int>(1 + log10((static_cast<double>(num))));
        divisor = static_cast<int>(pow(10,(static_cast<double>(numDigits) - 1)));
        while(divisor >= 1)
        {
            if((numCounter/divisor)==1)
            {
                ans = ans + pow(2,(static_cast<double>(numDigits)-1));
                numCounter -= divisor;
            }
            divisor /= 10;
            numDigits -= 1;
        }
        cout<<endl<<num<<" in decimal form is "<<ans<<endl<<endl
            <<"Convert another number?  (Y)es or (N)o."<<endl;
        cin>>again;
        cout<<endl<<endl<<endl;
    }while(toupper(again) == 'Y');
    return a.exec();
}

Thanks to anyone who bothered to look at this. I'm sure it's an eyesore.