Checking textbox for valid input in a loop or try catch c#

Question

I am having trouble validating user input, I have the following loop which definitely catches it but when the loop starts again the user doesn't have a chance to enter a different value so the value is the same and just creates an endless loop.

              private void guess_Click(object sender, EventArgs e)
    {


        int guessInt = 0;

        bool pass = false;
        int number;
        while (pass == false)
        {
            if (guessInput.Text != "")
            {
                pass = Int32.TryParse(guessInput.Text, out number);
                if (pass)
                {
                    guessInt = number;
                }
                else
                {
                    MessageBox.Show("You did not enter an integer, please enter a integer", "Invalid Values", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    guessInput.Text = "";
                }
            }
            else MessageBox.Show("You did not enter anything, please enter a integer", "Invalid Values", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
        guess.Enabled = false;
        next_Guess.Enabled = true;

        if (guessInt == randomArray[x])
        {
            result.Text = ("You Win! The correct number was " + randomArray[x]);
            right += 1;
            correctAnswers.Text = right.ToString();

        }
        else
        {
            result.Text = ("Sorry you lose, the number is " + randomArray[x]);
            wrong += 1;
            incorrectAnswers.Text = wrong.ToString();

        }

        hintLabel.Enabled = false;
        x++;
    }

So how can the user have a chance to reenter a value and the loop start again or should I be using a try/catch attempt here?

have you tried braking the loop with break; and then start the loop again when user enters a different value. — Writwick
– Writwick, Commented May 16, 2012 at 3:29
@I.am.WritZ, if I break the loop, especially during a failed attempt or the else portion I don't want to continue after the loop with a invalid entry. — programmerNOOB
– programmerNOOB, Commented May 16, 2012 at 3:33
So break the loop and return the void or you can maintain a bool which will hold the success/fail of the loop. — Writwick
– Writwick, Commented May 16, 2012 at 3:37

Damith · Accepted Answer · 2012-05-16 04:22:22Z

1

int number;
if(string.IsNullOrEmpty(guessInput.Text))
{
  MessageBox.Show("You did not enter an integer, please enter a integer", "Invalid Values", MessageBoxButtons.OK, MessageBoxIcon.Error);
  return;
}
if(Int32.TryParse(guessInput.Text, out number))
{
  guessInt = number; 
}else
{
  MessageBox.Show("You did not enter an integer, please enter a integer", "Invalid Values",      MessageBoxButtons.OK, MessageBoxIcon.Error);
   guessInput.Text = "";
   return;
}


// when come to here you have guessInt, process it 

   guess.Enabled = false;
    next_Guess.Enabled = true;

    if (guessInt == randomArray[x])
    {
        result.Text = ("You Win! The correct number was " + randomArray[x]);
        right += 1;
        correctAnswers.Text = right.ToString();

    }
    else
    {
        result.Text = ("Sorry you lose, the number is " + randomArray[x]);
        wrong += 1;
        incorrectAnswers.Text = wrong.ToString();

    }

    hintLabel.Enabled = false;
    x++;

edited May 16, 2012 at 4:22

answered May 16, 2012 at 3:47

Damith

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1 Comment

programmerNOOB Over a year ago

That did it, I just needed a nested if to cover all my grounds, thank you!

Ivo · Accepted Answer · 2012-05-16 04:03:47Z

1

It seems you don't need a while there:

          int number;

          if(guessInput.Text != "")
          {
              var pass = Int32.TryParse(guessInput.Text, out number);
              if (pass)
              {
                 guessInt = number;        
              }
              else
              {
                 MessageBox.Show("You did not enter an integer, please enter a integer", "Invalid Values", MessageBoxButtons.OK, MessageBoxIcon.Error);
                 guessInput.Text = "";
              }
           }

if you want to validate also for empty values, just remove the first if:

          int number;

          var pass = Int32.TryParse(guessInput.Text, out number);
          if (pass)
          {
             guessInt = number;        
          }
          else               {
             MessageBox.Show("You did not enter an integer, please enter a integer", "Invalid Values", MessageBoxButtons.OK, MessageBoxIcon.Error);
             guessInput.Text = "";
          }

edited May 16, 2012 at 4:03

answered May 16, 2012 at 3:32

Ivo

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7 Comments

programmerNOOB Over a year ago

I could play with this but the problem is that if the input is not blank it just skips it all and the input is never assigned to the value I need.

programmerNOOB Over a year ago

this is a portion within a button click method where the user enters a number in a textbox and presses this button and I am trying to validate it.

Ivo Over a year ago

Great. So, what is wrong with the code I've provided? If the text is something, it parses it and checks if it's a valid number. if not, it shows the text and blanks the textbox. It seems ok.

programmerNOOB Over a year ago

how do I account for a blank entry then?

Ivo Over a year ago

You want to validate it? just remove the first if. I'll update the code for that

|

Tass · Accepted Answer · 2012-05-16 03:36:47Z

As soon as the user clicks OK on the messagebox, the loop is going to run again without giving the user a chance to change the value.

What you need to do is run validation only when they enter a guess. That is, rather than have a loop, have some code that is triggered by an event (such as clicking a button) or by the validation callback provided by winforms.

Here's an example and short article I found on using the validation callback: http://blog.scosby.com/post/2010/02/11/Validation-in-Windows-Forms.aspx

In that example, see:

private void buttonSave_Click - this is where you would put your messagebox, and
private void textBoxNumber_Validating - this is where you would put your pass = Int32.TryParse(guessInput.Text, out number)... code.

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