DO_WHILE

 Executes a block of statements repeatedly until the value of a
 logical expression is false.  Statement format:

    DO [s][,] WHILE (e)

    s  Is the label of an executable statement which follows 
       the DO statement in the same program unit. The label 
       designates the last statement of the DO loop. If 
       omitted, an END DO statement is required.

    e  Is a logical expression.  You can reference and modify 
       the variable elements of the expression within the 
       DO loop.

 You can transfer control out of a DO WHILE loop but not into a loop
 from elsewhere in the program.

 The DO WHILE statement tests the logical expression at the
 beginning of each execution of the loop, including the first.  If
 the value of the expression is true, the statements in the body of
 the loop are executed; if the expression is false, control
 transfers to the statement following the loop.

 If no label appears in the DO WHILE statement, the DO WHILE loop
 must be terminated with an END DO statement.