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I'm trying to us Alphanumeric Values in a textbox. The box must contain 4 characters. No more or less. While my code below will work for Alphanumeric. I can't get it to recognize 4 characters.
Can you help?

What I have tried:

public void AlphaNumericString()
       {

           //string value;
           string s = BacBox.Text.ToString();
           int.TryParse(s, out int result);


           Regex r = new Regex("^[a-zA-Z0-9]*$");
           if (r.IsMatch(s) && (s.Length > 3  && s.Length< 5 ))
           {

                   BacBox.Text = s;

           }
          else
           {
               MessageBox.Show("Enter 4 alphanumeric characters only");
           }


       }
Posted
Updated 28-Nov-17 10:48am
Comments
Richard Deeming 30-Nov-17 13:56pm
   

Try:
^[a-zA-Z0-9]{4}$

Get a copy of Expresso[^] - it's free, and it examines and generates Regular expressions.
   
   
Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[^]
Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[^]
Expresso Regular Expression Tool[^]
RegExr: Learn, Build, & Test RegEx[^]
This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx:
Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[^]
   

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