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?](https://stackoverflow.com/questions/5131647/why-would-we-call-cin-clear-and-cin-ignore-after-reading-input) — VLL, Aug 15 '18 at 12:01

score 4 · Accepted Answer · edited May 23 '17 at 12:14

4

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.

edited May 23 '17 at 12:14

Community

1
1

answered Oct 16 '15 at 11:25

Vladimir Svyatski

460
2
6

Thanks!, now works. I was trying with cin.clear(); and cin.ignore(); But no idea what that "1000" does inside cin.ignore. Now I have a path to follow. Thanks for the code and for the link!. – Reaversword Oct 16 '15 at 11:37

score 0 · Answer 2 · answered Oct 16 '15 at 10:49

0

if user input a character than it will take the ascii value of character so it will not stop. To stop the loop enter 0.

answered Oct 16 '15 at 10:49

Hmmm?. I'm using Visual Studio 2015. The behaviour I can observe is: Enter a number (even 0) > I get message "thanks", but if enter a character, message "Please, enter a number" repeats forever. – Reaversword Oct 16 '15 at 11:08

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

2 Answers2

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