DO: first statement of a loop

• The DO loop controls the repeated execution of a block of statements or constructs
• The loop variable loopvar is set to loopstart to loopend in steps of loopstep (default is 1):
• loopstart, loopend, and loopstep are numerical values or expressions

   DO loopvar = loopstart, loopend, loopstep ! loopstep=1 can be omitted 
      ! ... block of statements or constructs
   ENDDO
   ! the terminating statement of a DO loop
  

• Alternatively, a DO loop can be written with a terminating label (e.g. 999):

   DO 999 loopvar = loopstart, loopend, loopstep ! loopstep=1 can be omitted 
      ! ... block of statements or constructs
   999 CONTINUE

  This allows a GOTO to the last (non executable) CONTINUE statement. This is not recommended, better is the use of an IF construct.
• There are simple loop operations, that can be programmed more efficiently by array operations.
• To exit a loop prematurely a RETURN, GOTO, or a function error exit can be programmed
• ⇒ Programming (loops)