Logical error with input validation in c++

Question

The following code contains a logical error every time i run it and enter 1 or 0 the code in the while loop is still executed. can someone tell me why?

bool getmove()
{
    bool move;
    cout << "Would you like to make the first move?(1 for yes 0 for no)\n";
    cin >> move;
    while(move != 1 || move != 0 || !cin.good())
    {
        if(!cin.good())
        {
            cout << "ERROR please try again\n";
            cin.clear();
            cin.ignore(80,'\n');
            cin >> move;
        }
        else
        {
            cout << "Invalid input please try again\n";
            cin >> move;
        }
    }
    return move;
}

Beta · Accepted Answer · 2012-10-23 02:41:51Z

1

Look at this line:

while(move != 1 || move != 0 || !cin.good())

It will always be the case that move != 1 || move != 0 (because it can't be both).

Furthermore, you'll avoid some trouble by reading in something like a string and testing that, rather than relying on casting.

answered Oct 23, 2012 at 2:41

Beta

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1 Comment

user1767077 Over a year ago

Thank you so much i dont know how i missed that. i could do: while((move != 1 && move !=0 ) || !cin.good)

Ryan · Accepted Answer · 2012-10-23 03:02:04Z

1

If you're trying to write a function which can validate the input of a boolean value, your code can be simplified to:

bool getmove()
{
    bool move;
    cout << "Would you like to make the first move?(1 for yes 0 for no)\n";
    while (!(cin >> move))
    {
        cout << "Invalid input please try again\n";
        cin.clear();
        cin.ignore(80, '\n');
    }
    return move;
}

It is important to realize that while (!(cin >> move)) will repeat the loop until a valid boolean value can be read from the console and written into move.

answered Oct 23, 2012 at 3:02

Ryan

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