How Can I Validate Integer Input in C ?

Checking Integer Input Stream in C

In C , verifying user input to ensure it's an integer can be challenging. This article demonstrates two methods to achieve this validation.

Method 1: Checking Input Failure

To check if input is an integer, use the following snippet:

int x;
cin >> x;

if (cin.fail()) {
    // Not an integer
}

If the entered value cannot be converted to an integer, cin.fail() returns true, indicating a non-integer input.

Method 2: Continuously Prompting for Integer Input

To repeatedly prompt for an integer until a valid input is entered, use this code:

int x;
std::cin >> x;
while (std::cin.fail()) {
    std::cout << "Error" << std::endl;
    std::cin.clear();
    std::cin.ignore(256, '\n');
    std::cin >> x;
}

The while loop continues until a valid integer is entered, clearing and ignoring previous invalid inputs.

Example

Consider the following code:

int firstvariable;
int secondvariable;

cout << "Please enter two integers and then press Enter:" << endl;
cin >> firstvariable;
cin >> secondvariable;

Using either of the methods described above, you can check if firstvariable and secondvariable are integers and handle non-integer inputs appropriately.

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