Help with obtaining a number from cin

[Tune42]

Here's the snippet from my code

cin >> balance;
    while (isdigit(balance))
    {
        cout << "\n" << balance << " is not a valid balance.";
        cout << "\nEnter the beginning balance: ";
        cin >> balance;
    }

The while loop seems to work in the sense that the code runs correctly afterwards if it is an actual number typed in. If a letter, like 'r', is entered instead of a number it's almost as if the buffer fills up and somehow skips the while loop above, getting stuck in an infinite loop that comes later in the program. I will post the full code if it would be helpful, but I basically just need a way to force the user to enter a number and not a letter or string

edit:

When I modify the code to this:

while (!(cin >> balance))
    {
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
        cout << "\nInvalid input. Please try again.";
        cout << "\nEnter the beginning balance: ";
        cin >> balance;
    }

It appears to give the error correctly when a letter is typed but for some reason entering a number makes the program wait until a second number is entered that it then uses for my variable balance.

edit2:

This appears to work

cout << "\nCheckbook Balancing Program\n\n";
    cout << "Enter the beginning balance: ";
    while (!(cin >> balance))
    {
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
        cout << "Invalid input. Please try again.";
        cout << "\n\nEnter the beginning balance: ";
    }

But I'm not clear on why when there's no line asking for the input between the prompt for the beginning balance and the while loop :/

[jlb]

In the following code you are asking for the balance twice, once in the while loop condition, and again at the end of the loop.

while (!(cin >> balance)) // Retrieve the balance from the user.
    {
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
        cout << "\nInvalid input. Please try again.";
        cout << "\nEnter the beginning balance: ";
        cin >> balance;  // Retrieve the balance from the user again.
    }

In your last snippet you only have one cin, the one in the while condition. Because you only have one cin statement your program should work correctly.

Jim

[Tune42]

Thank you for your reply. I've taken some VERY elementary courses in C and java and never asked for any input in a loop condition. It makes sense the way you put it though, Thanks a bunch