How to keep_window_open() not working depending on inputs

Question

I ran the following code twice.

Once when I input Carlos 22, the program ran correctly and keep_window_open() apparently worked as the console

Answer 1

This is caused by invalid input to cin.

You can add error handling to avoid such issue by following:

change

cin >> first_name >> age;
cout << "Hello, " << first_name << " (age " << age << ")\n";

to

cin >> first_name;
while (!(cin >> age)) {
  cout << "Invalid age, please re-enter.\n";
  cin.clear();
  cin.ignore(std::numeric_limits::max(), '\n');
}