Recently I needed to validate a string input by a user to ensure it was in a specific format. One of the requirements was that after the first character, all of the rest of the input must be numeric. Here is how you can accomplish this:
string tag = “S127437”; //Your input string goes here
alphatag = tag.Substring(1,tag.Length-1);
bool isalpha = double.TryParse(alphatag, out Num);
Using the TryParse function allows you to see if a passed in string will convert properly into the Double datatype. An easy bit of code to use to validate for a numeric input.