FOR…NEXT
Execute a block of statements a specified number of times
Syntax
FOR <idCounter> := <nStart> TO <nEnd> [STEP <nIncrement>]
<statements>...
[EXIT]
<statements>...
[LOOP]
NEXT
Arguments
<idCounter> is the name of the loop control or counter variable. If the specified <idCounter> is not visible or does not exist, a private variable is created.
<nStart> is the initial value assigned to <idCounter>. If <nIncrement> is negative, <nStart> must be less than <nEnd>.
TO <nEnd> defines the final value of <idCounter>. If <nIncrement> is negative, <nStart> must be greater than <nEnd>; otherwise, <nStart> must be less than <nEnd>.
STEP <nIncrement> defines the amount <idCounter> is changed for each iteration of the loop. <nIncrement> can be either positive or negative. If the STEP clause is not specified, <idCounter> is incremented by one for each iteration of the loop.
EXIT unconditionally branches control from within a FOR…NEXT construct to the statement immediately following the nearest NEXT statement.
LOOP branches control to the most recently executed FOR or DO WHILE statement.
Description
FOR…NEXT is a control structure that executes a block of statements a specified number of times. The control structure loops from the initial value of <idCounter> to the boundary specified by <nEnd>, moving through the range of values of the control variable for an increment specified by <nIncrement>. All expressions in the FOR statement are reevaluated for each iteration of the loop. The <nStart> and <nEnd> expressions, therefore, can be changed as the control structure operates.
A FOR loop operates until <idCounter> is greater than <nEnd> or an EXIT statement is encountered. Control then branches to the statement following the corresponding NEXT statement. If a LOOP statement is encountered, control branches back to the current FOR statement.
If <nIncrement> is a negative value, <idCounter> is decremented rather than incremented. The FOR loop, however, continues until <idCounter> is less than <nEnd>. This means that <nEnd> must be less than <nStart> when the FOR loop begins.
FOR loops are useful for traversing arrays where <idCounter> is used as the array subscript. See the example below.
FOR…NEXT constructs may be nested within any other control structures to any depth. The only requirement is that each control structure is properly nested.
Examples
. This example traverses an array in ascending order:
nLenArray := LEN(aArray)
FOR i := 1 TO nLenArray
<statements>...
NEXT
. To traverse an array in descending order:
nLenArray := LEN(aArray)
FOR i := nLenArray TO 1 STEP -1
<statements>...
NEXT
Seealso
AEVAL(), BEGIN SEQUENCE, DO CASE, DO WHILE, IF, IF()