In C#, how can I use Regex.Replace to add leading zeroes (if possible)?

Question

I would like to add a certain number of leading zeroes to a number in a string. For example:

Input: \"page 1\", Output: \"page 001\" Input: \"page 12\", Ouput: \"pa

Answer 1

string sInput = "page 1 followed by page 12 and finally page 123";

string sOutput = Regex.Replace(sInput, "[0-9]{1,2}", m => int.Parse(m.Value).ToString("000"));