using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string[] partNumbers= { "1111-111-1111"};
string pattern = @"^[a-zA-Z0-9]\d{2}[a-zA-Z0-9](-\d{3}){2}[A-Za-z0-9]$";
foreach (string partNumber in partNumbers)
Console.WriteLine("{0} {1} a valid part number.",
partNumber, Regex.IsMatch(partNumber, pattern) ? "is" : "is not");
}
}