How to restrict user from entering digits after decimal point in the text box in C#

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Hi,
i have an text box which accepts numeric and decimal values.The text box allows only one digit after the decimal point.Max length of text box is 4.

now when the text box contains a text as ".8", how can i restrict user from entering digits after a decimal point(i.e when cursor position is immediately after the decimal point).

At the same time i should allow max of two digits before the decimal point

ex:
1.2---?valid
12.3---->valid
.78--->invalid
.768--->invalid

So how can i set the cursor position so that it will allow user to enter max of two digits before the decimal point and restrict user from entering digits after the decimal point when there is already a single digit after the decimal point(like ".8").

Posted 17-Mar-14 20:47pm

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Peter Leow · Answer 1 · 2014-03-17T21:14:00

You can use Regex to detect input discrepancy, adapt from this example:

C#

using System;
using System.Text.RegularExpressions;
public class Program
{
    public static void Main()
    {
        string input = "12.3";

        Regex regex = new Regex(
             "^\\d{0,2}[.]\\d$",
             RegexOptions.IgnoreCase
            | RegexOptions.CultureInvariant
            | RegexOptions.Compiled
        );

   if (regex.IsMatch(input))
      {
          // do something
          Console.WriteLine("Valid");
      }
        else
        {
            // do other thing
            Console.WriteLine("Not valid!");
        }
    }
}