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.

[GCDEF]

[] are used to wrap the code tags, not <>

If you want a bigger binary number, read it into a char array or string.

I'd just use an if statement to determine if each character was a 1 or a 0 and return an error if it isn't.

[getajob92]

I'm not allowed to use to use strings, and I've never used an array before.

Thanks to whoever gave me editing power!

[GCDEF]

Can't you edit your post?

[Lindley]

The only way to support a longer input without using some kind of string (either a string class or a char array) would be to use a larger integer type. Try "long long", which is 64 bits on most machines.

[getajob92]

Can't you edit your post?

Nope :-(. Even in my "Posting Rules" it says "You may not edit your posts."

-Edit- Now I can! Dunno why I couldn't before, but all good now!

The only way to support a longer input without using some kind of string (either a string class or a char array) would be to use a larger integer type. Try "long long", which is 64 bits on most machines.

I'll try that and get back right away!

[Peter_B]

There is no need to read the entire input into either a string, array or int before processing it. You can simply treat the input as a 'stream' of characters, and do whatever processing you need to do upon reading each one.

Outline code for this would be:

do {
	const int c = getchar(); // Get the next character from the input

	// Take the appropriate steps depending upon this character
	// I.e. if it is EOF or newline, stop the loop

	// If it is not either 0 or 1, report an error
	// (or set an error code for later code to check)

	// If it is 0 or 1, use it to build up the number
} while (true);

It would also be a good idea to check that the user isn't entering so many digits that the number would overflow whatever int type you use to store the number.

[getajob92]

I tried long long, but anything past 10 1s would still break the program. It didn't, however, crash the console, so that was a start.

I've never used getchar before, but I know it's incredibly useful so I'll play around with it and get back to ya.

And yeah, I'll probably figure out a way to stop them from causing the overflow.