while

 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.