ACR Electronics FPR-10 PROGRAMMER Manual descarregar pdf (Página 54)

Parker Hannifin

54 Programmer’s Guide

Repetition

The repetition structure—known as a loop—controls the repeated

execution of a statement or block of statements.

While the conditions remain true, the program loops (or iterates)

through the specific code. Typically, the repetition structure includes

a variable that changes with each iteration. And a test of the value

determines when the conditions of the expression are satisfied. The

program then moves to the next statement past the repletion

structure.

If the condition is not met, the loop does not execute. In many cases

that is acceptable behavior. Conversely, if the condition is always

met, then the loop does not end. An endless loop is probably not a

desired result, so be mindful when writing the loop conditions.

AcroBASIC also provides the following looping statements:

• FOR/TO/STEP/NEXT

• WHILE/WEND

FOR/TO/STEP/NEXT

When you expect to loop through a block of code for a number of

times, the FOR/NEXT loop is a good choice. It contains a counter, to

which you assign starting and ending values. You also assign a STEP

value (positive direction only), the value by which the counter

increments.

When the FOR/NEXT loop executes the first time, the end value and

the counter are compared. If the current value is past the end

value, the FOR/NEXT loop ends and the statement immediately

following executes. Otherwise, the statement block within the

FOR/NEXT loop executes.

On each encounter of the NEXT statement, the counter increments

and loops back to the FOR statement. The counter is compared to

the end value with each loop. When the counter exceeds the end

value, the loop skips the statement within, and proceeds to execute

the statement immediately following the FOR/NEXT statement.

You can exit a FOR/NEXT loop before the counter is complete using

a BREAK statement. When the condition is met, the statement

immediately following the FOR/NEXT loop executes.

Example

The following demonstrates a FOR/NEXT loop with a BREAK

statement.

FOR LV0 = 0 TO 499 STEP 1

PRINT LA0(LV0), SA0(LV0)

DWL 0.01

IF (BIT 24)

BREAK

ENDIF

1 2 ... 49 50 51 52 53 54 55 56 57 58 59 ... 198 199

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