Member Avatar for Asus93 
while (!correct)
        {   

            cout << "Please enter an angle value => ";
            cin >> value; //request user to input a value

            if(cin.fail())
            {
                cin.clear();
                while(cin.get() != '\n');
                textcolor(WHITE);
                cout << "Please enter a valid value. "<< endl;
                correct = false;

            }
            else
            {
                cin.ignore();
                correct =true;
            }
        }

Hi, this is part of the code that I have written.
The purpose of this code is to restrict users to input numbers like 10,10.00 etc,
if they input values like (abc,!$@,etc...) the code will request users to reenter the values.

In order to perform this function( restrict user to input valid valus), I get some tips and guides through forums.

I think is my responsibility to learn and understand what these codes do... since this is the first time I use this code.
can someone briefly explain to me what does these codes mean in the program:
cin.fail() cin.clear() while(cin.get() != '\n') cin.ignore()

Thanks for your guides, I appreciate that!

  • 2 Contributors
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  • 2 Hours Discussion Span
  • Latest Post Latest Post by Ancient Dragon

Dani AI

Generated

A short, practical explanation that fills the gaps in the existing snippets.

Operator>> attempts to parse the next token from the input as the requested type. If parsing fails (for example the user types letters when a number is expected) the extraction sets the stream’s fail state and the stream evaluates as false. Detecting that state with cin.fail() is the normal way to know the extraction failed. (en.cppreference.com)

cin.fail() returns true when either failbit or badbit is set; cin.clear() resets the stream error flags (by default to goodbit) so further operations can run. Important: clear() does not remove the invalid characters that caused the failure — you still need to remove them from the input buffer before trying again. (en.cppreference.com)

The loop while(cin.get() != '\n') reads and discards characters one at a time until a newline (that is what described). That works, but the idiomatic and clearer approach is to discard the rest of the line in one call using ignore() with numeric_limits::max() as the count so it stops at the newline; this avoids leaving junk in the buffer and handles very long input safely. get() and ignore() have slightly different behaviors on EOF and error conditions, so prefer ignore(max, '\n') for line flushing. (cppreference.com)

Example pattern (safe, minimal change from your logic — does not use the exact code in the thread):

#include <iostream>
#include <limits>

double read_number() {
    double v;
    while (true) {
        std::cout << "Enter angle: ";
        if (std::cin >> v) {
            std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
            return v;
        }
        std::cin.clear(); // clear failbit
        std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // discard bad input
        std::cout << "Please enter a valid numeric value.\n";
    }
}

Notes and cautions: calling cin.ignore() with no arguments discards only one character — that’s why the ignore(max, '\n') form is preferred after clear(). For more complex validation consider std::getline() + parsing the whole line (e.g., std::stringstream or std::stod) so you fully control what’s accepted. (en.cppreference.com)

Member Avatar for Ancient Dragon

You will find the explanation of them all here

while(cin.get() != '\n')

The above is getting characters from the keyboard one at a time until '\n' (Enter key) is reached.

Edited by Ancient Dragon
commented: Good link, C++.com - I keep a tab open to it in my browser all the time! :-) +12
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