I've used atoi() in my code already, so I will use itoa() to go the other way. and the format function won't help. The variable has to be a const char* to be used in one of the functions, so I have to convert it. Casting it gives a run-time read error.
Maybe I'm missing something, but why don't you just read the user's input as an integer?
cout << "Enter a four digit number immediately: ";
(cin >> entry).get();
cout << "Yo stupid, I said enter a fo' digit numbah son!" << endl;