Validating that the user does not enter a decimal in C#

Question

if (double.TryParse(txtDays.Text, out days) == false)
{
   MessageBox.Show("Enter a whole number for days.", Text, MessageBoxButtons.OK, MessageBoxIcon.Information);
   txtDays.Focus();
   return;
}

I'm a newbie at C# so any help would be appreciated :)

What is your question exactly? You said `decimal` in your title but parsed `double` in your example. And just `if (decimal.TryParse(txtDays.Text, out days))` would seems better.. — Soner Gönül, Mar 09 '15 at 15:48
How about using a numeric up/down control rather than a textbox? — Trevor Pilley, Mar 09 '15 at 15:50
Also, if you want to ensure whole values only and want to continue using a textbox, why not use `if(!int.TryParse(...)`? — Trevor Pilley, Mar 09 '15 at 15:51
Seconding @TrevorPilley comment. Why not just use an `int` instead? — sab669, Mar 09 '15 at 15:55

Tim Schmelter · Answer 1 · 2015-03-09T16:44:31.150

You want to prevent that the user enters a decimal-separator? So he is allowed to use integers only? Then don't try to parse to double but to int:

if (!int.TryParse(txtDays.Text.Trim(), out days))
{
   MessageBox.Show("Enter a whole number for days.", Text, MessageBoxButtons.OK, MessageBoxIcon.Information);
   txtDays.Focus();
   return;
}

Maybe it's even better to use uint.TryParse since that prevents the - sign, but that depends on if negative days are possible.

But you should consider to use the NumericUpDown-control

score 0 · Answer 2 · edited May 23 '17 at 12:22

0

There are multiple approaches and all are covered here:
How do I make a textbox that only accepts numbers?

Most common approach is to use a NumericUpDown control rather than a TextBox.

If you want a message box, Tim's answer is pretty much exactly what you need.

edited May 23 '17 at 12:22

Community

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answered Mar 09 '15 at 16:12

bokibeg

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score -1 · Answer 3 · edited May 23 '17 at 11:50

-1

You would be better to use a regular expression to check for this I suspect. The following code:

Regex regex = new Regex(@"^\d$");

will check that the string is an integer, well actually it checks that a single digit is an integer, the link below shows how to amend it to check a full string.

(The code comes from this question: Regex for numbers only)

edited May 23 '17 at 11:50

Community

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answered Mar 09 '15 at 15:51

Pheonyx

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Regex for decimal parsing? o.O – Soner Gönül Mar 09 '15 at 15:54
@SonerGönül, no to confirm that what is entered is an integer not a decimal as per his "Validate user does not enter a decimal". If it passes the regex then it is valid, else it's not. – Pheonyx Mar 09 '15 at 15:55

Validating that the user does not enter a decimal in C#

3 Answers3