SaleenS7 SaleenS7 - 1 year ago 102
C++ Question

How is this an infinite loop?

I wrote this program for an intro to comp sci class. All it is is a demonstration of using a while loop. My professor marked this program as having an infinite loop, but I don't understand how it is an infinite loop because it terminates when -1 is entered.

int main() {

int accountNum, balance, totalOfItems, totalOfCredits, creditLimit; //Integers for the user to input

while (accountNum != -1)
cout << "Enter account number" << endl;
cin >> accountNum;
cout << "Enter balance" << endl;
cin >> balance;
cout << "Enter total of all items charged this month" << endl;
cin >> totalOfItems;
cout << "Enter total of all credits applied to the account this month" << endl;
cin >> totalOfCredits;
cout << "Enter credit limit" << endl;
cin >> creditLimit;

int newBalance = balance + totalOfItems - totalOfCredits;

if (newBalance > creditLimit)
cout << "Account Number: " << accountNum << "\nCredit Limit: " << creditLimit << "\nNew Balance " << newBalance << endl;
cout << "Credit limit exceeded." << endl;
} else {
cout << "New balance : " << newBalance << endl;
return 0;

Answer Source

There are multiple bugs in the shown code.

  1. accountNum is not initialized, before it is used. This results in undefined behavior.

  2. Even if -1 is entered, the loop will still slog through, and all the remaining input must still be entered.

  3. If invalid input is entered, std::cin enters error state, and will loop forever.

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