step 1: Syntax While Loop

  1. While (condition)
  2. {
  3. //Execute Statament
  4. }
step 2: Logic Binary Number

  1. protected void Button1_Click(object sender, EventArgs e)
  2. {
  3. int intNo = Convert.ToInt32(txtNo.Text.Trim());
  4. int intBinary;
  5. string strBinary = "";
  6. while (intNo != 0)
  7. {
  8. intBinary = intNo % 2;
  9. intNo = intNo / 2;
  10. strBinary = intBinary + strBinary;
  11. }
  12. //strBinary.Reverse();
  13. lblBinaryNo.Text = strBinary;
  14. }

You can implement while loop concept and modulo and division operation easily.