Use program loops

Loops allow you to execute a section of code repeatedly. The InTouch HMI only supports FOR loops. A FOR loop works by monitoring the value of a numeric loop variable that is incremented or decremented with each loop iteration. The loop is executed until the value of the loop variable reaches a fixed limit.

Syntax

FOR LoopTag = StartExpression TO EndExpression [STEP ChangeExpression]

... statements or another FOR loop ...

NEXT;

• StartExpression, EndExpression and ChangeExpression together define the number of iterations.

• StartExpression sets the start value of the loop range. EndExpression sets the end value of the loop range.

• STEP ChangeExpression optionally sets the value by which the loop tag is incremented or decremented during each loop iteration; if you do not specify this, a default of 1 is used.

When you execute a FOR loop, the InTouch HMI:

1. Sets LoopTag to the value of StartExpression.

2. Tests whether LoopTag is greater than EndExpression. If so, the InTouch HMI exits the loop. (If ChangeExpression is negative, the InTouch HMI tests whether LoopTag is less than EndExpression.)

3. Executes the statements within the loop.

4. Increments LoopTag by the value of ChangeExpression (1 unless otherwise specified).

5. Repeats steps 2 through 4.

Remember the following rules when working with FOR loops:

• FOR loops can be nested. The maximum number of nesting levels depends on the available memory and system resources.

• For every FOR statement, there must be a closing NEXT statement. A NEXT statement always applies to the nearest prior FOR statement on the same nesting level.

• LoopTag must be a numeric tag (or local variable).

• StartExpression, EndExpression and ChangeExpression must be valid expressions that evaluate to a numeric result.

• If ChangeExpression is positive, EndExpression must be greater than StartExpression; if ChangeExpression is negative, StartExpression must be greater than EndExpression. Otherwise, the loop does not start.

• To exit a loop, use the EXIT FOR statement. For more information, see Force the end of a loop.

• There is a time limit for loops. See Time limit for loop execution.

  Caution: Loop execution affects other run-time processes. For more information, see Effect of loops on other run-time processes.