C++ character to int

Question

what happens when you cin>> letter to int variable? I tried simple code to add 2 int numbers, first read them, than add them. But when I enter letter, it just fails and prin

Answer 1

I assume you have code like this:

int n;
while (someCondition) {
    std::cin >> n;
    .....
    std::cout << someOutput;
}

When you enter something that cannot be read as an integer, the stream (std::cin) enters a failed state and all following attempts at input fail as long as you don't deal with the input error.

You can test the success of an input operation:

if (!(std::cin >> n)) //failed to read int

and you can restore the stream to a good state and discard unprocessed characters (the input that caused the input failure):

std::cin.clear();
std::cin.ignore(std::numeric_limits::max(), '\n');

Another possibility is to accept input into a string variable (which rarely fails) and try to convert the string to int.

This is a very common problem with input and there should be tons of threads about it here and elsewhere.