only problem with this program is that when I enter 'z' to exit it works but when I try'Z' it does not work. pls help




using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace assignment2_nepal
{
    class sales
    {
        public char empname;
        Double indsale;
        Double indsaleA = 0;
        Double indsaleB = 0;
        Double indsaleE = 0;
        Double indcomsaleA = 0;
        Double indcomsaleB = 0;
        Double indcomsaleE = 0;
        const Double commrate = 0.10;


        public void TotalSales()
        {

            Console.WriteLine("Enter A for Andrea or B or Brittany or E for Eric or z to quit:");
            Console.WriteLine("Enter a salesperson initial:");


            empname = Convert.ToChar(Console.ReadLine());

            while (empname !== 'z' || empname=='Z')
            {
              

                    if (empname == 'A' || empname == 'a')
                    {
                        Console.Out.WriteLine("Enter amount of sale");
                        indsale = Convert.ToDouble(Console.ReadLine());
                        indsaleA = indsaleA + indsale;
                    }
                    else if (empname == 'B' || empname == 'b')
                    {
                        Console.Out.WriteLine("Enter amount of sale");
                        indsale = Convert.ToDouble(Console.ReadLine());
                        indsaleB = indsaleB + indsale;
                    }
                    else if (empname == 'E' || empname == 'e')
                    {
                        Console.Out.WriteLine("Enter amount of sale");
                        indsale = Convert.ToDouble(Console.ReadLine());
                        indsaleE = indsaleE + indsale;
                    }
                    else
                        Console.Out.WriteLine("Invalid Entry! Please enter A, B or E for sales Employee and z to Quit");
                    Console.WriteLine("Enter another salesperson or z to quit");
                    empname = Convert.ToChar(Console.ReadLine());
                }
            }
      
        public void computesales()
        {
            indcomsaleA = commrate * indsaleA;
            indcomsaleB = commrate * indsaleB;
            indcomsaleE = commrate * indsaleE;
        }


        public void PrintSales()
        {
            Console.WriteLine("Andrea earned:               ${0}", indcomsaleA);
            Console.WriteLine("Brittany earned:             ${0}", indcomsaleB);
            Console.WriteLine("Eric earned:                 ${0}", indcomsaleE);
        }

    }
    class assignment2_nepal
    {
        static void Main(String[] args)
        {
            sales sale = new sales();
            sale.TotalSales();
            sale.computesales();
            sale.PrintSales();
        }

    }
}