How to Properly Validate Double Input in C ?

How to Validate User Input as a Double in C

When working with user input, it's crucial to validate the input to ensure its validity. In C , validating user input as a double can be achieved through various methods. One common approach is to use the cin operator, as demonstrated in the code snippet below:

double x;

while (1) {
    cout << ">";
    if (cin >> x) {
        // valid number
        break;
    } else {
        // not a valid number
        cout << "Invalid Input! Please input a numerical value." << endl;
    }
}

However, this code may encounter an issue where it continuously outputs the "Invalid Input!" statement, prohibiting it from prompting for another input. To address this, the following modification can be made:

...
else {
    // not a valid number
    cout << "Invalid Input! Please input a numerical value." << endl;
    cin.clear();
    while (cin.get() != '\n') ; // empty loop
}
...

This modification includes two essential steps:

1. Clearing the Error State: cin.clear() is used to clear the error state that was set when the invalid input was encountered. This allows the program to continue reading input without the error flag interfering.
2. Empty Loop: The while (cin.get() != 'n') ; loop is an empty loop that consumes the remaining characters that were entered on the same line as the invalid input. This ensures that any invalid characters are removed from the input buffer, and the program is ready to read the next input.

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