for

 The for statement executes a statement zero or more times, with
 three specified control expressions.  Expression-1 is evaluated
 only once, before the first iteration; expression-2 is evaluated
 before every iteration; expression-3 is evaluated after every
 iteration.  The for loop terminates if, on evaluation, expression-2
 is 0.
 Syntax:

      for ( [expression-1] ; [expression-2] ; [expression-3] )
          statement

 The for statement is equivalent to the following format:

      expression-1;
      while ( expression-2 ) { statement expression-3; }

 You can omit any of the three expressions.  If expression-2 is
 omitted, the while condition is true.