Lenze DDS v2.3 Manuel d'utilisateur télécharger pdf (Page 47)

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Programming languages

4-9

l DDS EN 2.3

4.3.10 WHILE loop

The WHILE loopcanbeusedlikeaFOR loop, the only difference being that the cancel condition can

be any Boolean expression.

Syntax:

WHILE <Boolean expression> DO

END_WHILE;

• The <instructions> will be executed again and again until the

<Boolean_expression> returns TRUE.

• If <Boolean_expression> is FALSE on first evaluation already, the <instructions> will

never be executed.

• If <Boolean_expression> is never FALSE the <instructions> will be repeated

endlessly, forcing a runtime error.

Note!

The programmer himself must ensure that endless loops do not occur by changing the condition

in the instruction part of the loop, for instance change the counter settings. Otherwise the task with

the endless loop would overflow.

Example:

WHILE Counter<>0 DO

Var1:=Var1*2;

Counter:=Counter-1;

END_WHILE

The WHILE and the REPEAT loops are more powerful in a way than the FOR loop since the number

of loop cycles does not need to be known prior to loop execution.

In some cases, these two loop types will have to be sufficient.

If the number of loop cycles is known, however, a FOR loop should be preferred.

Task overflows can also occur in FOR loops.

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Lenze DDS v2.3 Manuel d'utilisateur Page 47