The while statement executes a statement 0 or more times, as long
  as a stated condition is true.
  Syntax:

       while ( expression ) statement

  The expression is evaluated before each execution, and the
  statement is executed if the expression is not 0.  The statement
  following the parentheses (the body of the while statement) is not
  optional; the null statement (a lone semicolon) is provided for
  specifying a while statement with an empty body.