Textbox input validation

[whirlwind2k8]

Hello all,

C# Beginner needs help

I have wrote a small exercise program with 4 text boxes which required user to input only one of the 2 strings: y or n

Could someone kindly show me how to do a simple input validation so only y or n are valid responses

Thank you so much

[BigEd781]

Sounds like homework. What have you tried already? What was the problem with that code?

[whirlwind2k8]

Thanks for reply

The following codes get checked by button click

if (((ans1TxBox.Text != y) || (ans1TxBox.Text != n)) ||
((ans2TxBox.Text != y) || (ans2TxBox.Text != n)) ||
((ans3TxBox.Text != y) || (ans3TxBox.Text != n)) ||
((ans4TxBox.Text != y) || (ans4TxBox.Text != n)))
{
MessageBox.Show("Please answer y or n in all 4 textboxes!");
ans1TxBox.Text = null;
ans2TxBox.Text = null;
ans3TxBox.Text = null;
ans4TxBox.Text = null;
ans1TxBox.Focus();
}

The message still pops up event when the input is correct

[MMH]

This looks interesting. Your condition seems to be proper logically, but it fails to validate the string with OR (||) operator.

If you check just for "y" or "n" at a time, it will work. Whereas it will fail to validate if used with OR.

Use regular expressions to solve this problem.

Use the following for regex.

using System.Text.RegularExpressions;

And the code:

private void btnCheck_Click(object sender, EventArgs e)
        {
            if (__isInputProper(textBox1.Text) || __isInputProper(textBox2.Text) ||
                __isInputProper(textBox3.Text) || __isInputProper(textBox4.Text))
            {
                MessageBox.Show("Please answer y or n in all 4 textboxes!");
                textBox1.Text = string.Empty;
                textBox2.Text = string.Empty;
                textBox3.Text = string.Empty;
                textBox4.Text = string.Empty;
                textBox1.Focus();
            }
        }

        private bool __isInputProper(string input)
        {
            return Regex.IsMatch(input.Trim(), @"[^yn]", RegexOptions.IgnoreCase);
        }

Set the max length of the TextBoxes to 1. Then this regex expression will work, Else you have to make another expression to handle other validations.

[JonnyPoet]

This looks interesting. Your condition seems to be proper logically, but it fails to validate the string with OR (||) operator.

Yes it fails this way it must fail this way. and
Noooooooooo this condition doesn't seem to be logically correct! This condition is per fact totally wrong .
It alsways will answer to 'false Input'. If you have a condition check for 'yes' or 'no' like here, then if you check in this way and you do 'yes' as an input so it is not 'no' at the same time logically !!

And because of that connecting both with 'or' operator || you will always fullfill the condition Putting in 'yes' will have a result true in the 'not no' part and putting in 'no' will result 'true' in the 'not yes' part.

Use regular expressions to solve this problem.

And that for a youngster who is just green in programming. Sounds like if you want a baby just has learned his first steps to walk on the Mount Everest

No stay simple. Dont use guns to shot an ant.
Simple use the correct statement Yes / no needs to be connected with AND while the different boxes are connected with OR so we have

if (((ans1TxBox.Text != y) && (ans1TxBox.Text != n)) ||
((ans2TxBox.Text != y) && (ans2TxBox.Text != n)) ||
((ans3TxBox.Text != y) && (ans3TxBox.Text != n)) ||
((ans4TxBox.Text != y) && (ans4TxBox.Text != n)))
{
MessageBox.Show("Please answer y or n in all 4 textboxes!");
ans1TxBox.Text = string.Empty;
ans2TxBox.Text = string.Empty;
ans3TxBox.Text = string.Empty;;
ans4TxBox.Text = string.Empty;;
ans1TxBox.Focus();
}

If you are talking very precise you will say: If it is not yes AND not no in the first OR the second OR the third OR the forth Textbox then I will write a message.

Note: texts in Textboxes are never null they are string.Empty when they dont contain text

[MMH]

Thanks "JonnyPoet" !
i sincerely appreciate that.