What is a regular expression to match only four digit numbers?

[Teresa Clark]

I am trying to find the syntax for using a regular expression to only match four digit numbers and there has to be at least one number. Any Ideas? :)

I have a form with a textbox and I am trying to using regular expression
matching to verify the form. I don't want the user to be able to leave the
textbox blank, it must be a real number from 0 to 9999. The user can't
leave the text box blank. The way it is working now is any number I put
in the textbox it is popping up the MessageBox "Enter a one to four digit
number!" If the user enters invalid data I want the button event to return
to the form method and stop executing.


Here's the code:

private void button2_Click(object sender, EventArgs e)
        {
 
            //invalid input checking
            if (regex_match(DelayA1Pulse6.Text))
            {
                return;
            }
    }
 
 
public static bool regex_match(string s)
        {
            Regex checkNumber = new Regex("/b/d{1,4}/b");
            if (checkNumber.IsMatch(s))
            {
                return false;
 
            }
            else
                MessageBox.Show("Enter a one to four digit number!");
                return true;
 
        }

The way it is working right now is any number I put in the textbox I am getting the error message box. I only want the message box to pop up when the user enters invalid input like 10000, blank, ASDF, 0100 etc.

[Rabbit]

A 4 digit number by definition has exactly 4 numbers and no other characters so I don't know what you mean by it must have at least one number. But the expression for that would be "/b/d{4,4}/b". If what you mean is a number with at least one digit and at most 4 digits then the expression would be "/b/d{1,4}/b".

[Rabbit]

You need to post your code in addition to any error messages you may have gotten along with test data and expected output.

[Rabbit]

Try replacing the / with \. I think I had the slashes mixed up.

[Teresa Clark]

I don't understand. Do I need to put ("\.b\.d{1,4}\.b");
in as the regular expression?

[Rabbit]

Get rid of the periods, the period was just to end the sentence.

[Teresa Clark]

Rabbit, It is giving me an error "Unregconized escape sequence"

[Rabbit]

Can you post the current regex you have?

[Teresa Clark]

Imade it work with "\\b\\d{1,4}\\b" Thanks for your help.