conditional.cs

using System;
   
class Program
{
   static void Main(string[] args)
   {
      try {
         DisplayFirstNumber(args);
      }
      catch (ArgumentException e) {
         Console.WriteLine(e.Message);
      }
   }
    
// <Snippet1>
   private static void DisplayFirstNumber(string[] args)
   {
      string arg = args.Length >= 1 ? args[0] : 
                                 throw new ArgumentException("You must supply an argument");
      if (Int64.TryParse(arg, out var number))
         Console.WriteLine($"You entered {number:F0}");
      else
         Console.WriteLine($"{arg} is not a number.");                            
     
   }
// </Snippet1> 
}