while loop to infinity when the input of a cin is a 'dot'

Question

I am having trouble using the cin method to acquire a variable. When the input is a number there is no problem, but when it is a special character like a dot [.], the whileloop

Answer 1

This example exactly reproduces your problem:

#include 

int main()
{
    int i = 5;
    while (i < 1 || i > 3)
    {
        std::cin >> i;
    }
}

Here's what happens: When operator>> fails to read an integer (e.g. when you type a dot and press enter), whatever you typed stays in the stream, including the newline character. So in the next iteration of the while loop the next input is already there and since it's not a valid integer, the loop can never break. You need to make sure that, when operator>> fails, you empty the stream and clear all the error flags that got set.

#include 
#include 

int main()
{
    int i = 5;
    while (i < 1 || i > 3)
    {
        if (!(std::cin >> i))
        {
            // clear streams internal error flags
            std::cin.clear();
            // ignore what's left in the stream, up to first newline character
            // or the entire content, whichever comes first
            std::cin.ignore(std::numeric_limits::max(), '\n');
        }
    }
}