Question

I have the following code to validate usernames for an application:

Regex usernameRegex = new Regex("[A-Za-z0-9_]");
if (usernameRegex.IsMatch(MyTextBox.Text)) {
    // Create account, etc.
}

How would I modify my regular expression to check if the username has a certain number of characters?

Answer 1

This expression validates only all text which contains any combination of A to Z, a to z and number 0 to 9. You can define the length of the string using the regex:

Regex reg= new Regex(@"^[A-Z]{3,}[a-z]{2,}\d*$")

{3,} and {2,} mean here that the string must have at least 3 capital characters, at least 2 small characters, and any amount of digit characters.

For example :
Valid : AAAbb, AAAbb2, AAAAAAbbbbb, AAAAAbbbbbb4343434

Invalid: AAb, Abb, AbAbabA, 1AAAbb,