DO: first statement of a loop

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⇒ Example of a DO call in "Loops/Nested" (RosettaCode)

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)