How to apply validation on an int variable so that it accepts only integer data and in case of any other data doesn't give an error?

Question

I want to limit the input of the user to integer data only. So I need to validate an integer variable to an extent that it accept only integer data and not alphabetic and special character data. For example, see the code below

int a;
cout << "Enter any number: ";
cin >> a;

Now if the user enter any data other than integer type. It should give the following output without any error

Enter any number: alphabet
Invalid Input! Try again..
Enter any number:

So how do i implement it?

Remy Lebeau · Answer 1 · 2017-07-06T15:36:44.527

0

The operator>> sets the stream's fail state if bad input is entered. You can test the stream's state after the read, eg:

#include <iostream>
#include <limits>

int a;
do
{
    std::cout << "Enter any number: ";
    if (std::cin >> a)
        break; // no error, a is valid
    std::cout << "Invalid Input! Try again.." << endl;
    std::cin.clear(); // reset error state
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // ignore any pending data
}
while (true);

// use a as needed...

edited Jul 06 '17 at 15:36

answered Jul 06 '17 at 07:03

Remy Lebeau

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is there any other way to do it? – IBTEHAAJ SHAHID Jul 06 '17 at 08:02
@IBTEHAAJSHAHID why? what's wrong with this way? – Remy Lebeau Jul 06 '17 at 08:36
I am using a header file stdlib.h. While using this header file, it gives an error at line 9 in your code i.e. `cin.ignore(numeric_limits::max(), '\n');` – IBTEHAAJ SHAHID Jul 06 '17 at 10:03
@IBTEHAAJSHAHID including `stdlib.h` only includes C library. You won't get `cin` nor `std::string`. If you want a C response, you should have tagged it as a C question. Try including `` – Guillaume Racicot Jul 06 '17 at 14:05
@IBTEHAAJSHAHID you shouldn't be using `stdlib.h` in C++ to begin with. Use `cstdlib` instead, if at all. And stay away from `using namespace std;`. I have updated my answer – Remy Lebeau Jul 06 '17 at 15:39
@Remy Lebeau Okay thanks – IBTEHAAJ SHAHID Jul 06 '17 at 17:37

How to apply validation on an int variable so that it accepts only integer data and in case of any other data doesn't give an error?

1 Answers1