while_loop.htm  also see do--while
    using System;
// csc while_loop_2.cs
class whileloop
{
public whileloop()
{ Console.WriteLine( "constructor evolved");}
 ~whileloop()
  { Console.WriteLine("destrctor evoked");}

    public int wl(int n)
    {
        int i = 0;

        while (i < n)
        {
            Console.Write("L="+ i + ",");
            i++;
        }
        Console.WriteLine();
        return i;
    }
} 
class test
{

static void Main()
{
whileloop w = new whileloop();
Console.Write("Enter a number  :" );
string str;
 str= Console.ReadLine();
try
{
//try block if correct wont show
int num = Int32.Parse(str);
w.wl(num);
Console.WriteLine("OK, carried On");

}
catch(Exception ex)

{
Console.WriteLine("looks like you missed something :"+
 str + " you may use ex to complete result"  );

}

}
}