Question

I Have a string in the form “123456789”.
While displaying it on the screen I want to show it as 123-456-789.
Please let me knwo how to add the “-” for every 3 numbers.
Thanks in Advance.

Answer 1

I’ll go ahead and give the Regex based solution:

string rawNumber = "123456789";
var formattedNumber = Regex.Replace(rawNumber, @"(\d{3}(?!$))", "$1-");

That regex breaks down as follows:

(        // Group the whole pattern so we can get its value in the call to Regex.Replace()
  \d     // This is a digit
  {3}    // match the previous pattern 3 times
  (?!$)  // This weird looking thing means "match anywhere EXCEPT the end of the string"
)        

The "$1-" replacement string means that whenever a match for the above pattern is found, replace it with the same thing (the $1 part), followed by a -. So in "123456789", it would match 123 and 456, but not 789 because it’s at the end of the string. It then replaces them with 123- and 456-, giving the final result 123-456-789.