while (reserved word)
 A while statement contains an expression that
 controls the repeated
 execution of a singular or compound statement.
 
  Syntax:
  while expression do statement
 
  Remarks:
 The statement after do is executed repeatedly
 as long as the
 Boolean expression is True.
 
 The expression is evaluated before the
 statement is executed, so if the
 expression is False at the beginning, the
 statement is not executed.
 
  Example:
  { "while" statements }
    while Ch = ' ' do Ch := GetChar;
 
   while not Eof(InFile) do
   begin
     ReadLn(InFile, Line);
     WriteLn(OutFile, Line);
     Inc(LineCount);
   end;