Why cin inside while doesn't stop to get user input?

Question

I'm starting now with C++, so I imagine this is gonna be a very easy-newbie question.

Well, why the "cin >> x" line inside while doesn't stop the loop to get the user input (if the user inputs a character, in place of a number)?

#include <iostream>
using std::cin;
using std::cout;
using std::endl;

int main()
{
    int x = 0;
    cout << "Please, enter x: ";
    cin >> x;
    while (!cin)
    {
        cout << "Please, it must be a number!\n";
        cin >> x;
    }
    cout << "Thanks!.";
    cin.ignore();
    cin.ignore();
}

I'm barely two days studiying C++, so I'm completely blind about what "cin" really is. I tried with "cin.sync()" and "cin.clear()", but still no luck. And I know it is impossible to do something like "cin=true", or "cout << cin".

Possible duplicate of Why would we call cin.clear() and cin.ignore() after reading input? — vll

Vladimir Svyatski Vladimir Svyatski · Accepted Answer · 2015-10-16T11:25:45

Well, your program should be corrected slightly

#include <iostream>
using std::cin;
using std::cout;
using std::endl;

int main()
{
    int x = 0;
    cout << "Please, enter x: ";
    cin >> x;
    while (!cin)
    {
        cin.clear();
        cin.ignore(10000, '\n');
        cout << "Please, it must be a number!" << endl;
        cin >> x;
    }
    cout << "Thanks!.";
}

This way it works as expected. More info about it here. In general, you need to clear all the errorneous stuff from cin.

Why cin inside while doesn't stop to get user input?

2 Answers