Loops

Remarks#

When looping over internal tables, it is generally preferable to ASSIGN to a field symbol rather than loop INTO a work area. Assigning field symbols simply updates their reference to point to the next line of the internal table during each iteration, whereas using INTO results in the line of the table being copied into the work area, which can be expensive for long/wide tables.

Internal Table Loop

LOOP AT itab INTO wa.
ENDLOOP.

FIELD-SYMBOLS <fs> LIKE LINE OF itab.
LOOP AT itab ASSIGNING <fs>.
ENDLOOP.

LOOP AT itab ASSIGNING FIELD-SYMBOL(<fs>).
ENDLOOP.

LOOP AT itab REFERENCE INTO dref.
ENDLOOP.

LOOP AT itab TRANSPORTING NO FIELDS.
ENDLOOP.

Conditional Looping

If only lines that match a certain condition should be taken into the loop, addition WHERE can be added.

LOOP AT itab INTO wa WHERE f1 = 'Max'.
ENDLOOP.

While Loop

ABAP also offers the conventional WHILE-Loop which runs until the given expression evaluates to false. The system field sy-index will be increased for every loop step.

WHILE condition.
* do something
ENDWHILE 

Do Loop

Without any addition the DO-Loop runs endless or at least until it gets explicitly exited from inside. The system field sy-index will be increased for every loop step.

DO.
* do something... get it?
* call EXIT somewhere
ENDDO.

The TIMES addition offers a very convenient way to repeat code (amount represents a value of type i).

DO amount TIMES.
* do several times
ENDDO.

General Commands

To break loops, the command EXIT can be used.

DO.
    READ TABLE itab INDEX sy-index INTO DATA(wa).
    IF sy-subrc <> 0.
        EXIT. "Stop this loop if no element was found
    ENDIF.    
    " some code
ENDDO.

To skip to the next loop step, the command CONTINUE can be used.

DO.
    IF sy-index MOD 1 = 0.
        CONTINUE. " continue to next even index
    ENDIF.
    " some code  
ENDDO.

The CHECK statement is a CONTINUE with condition. If the condition turns out to be false, CONTINUE will be executed. In other words: The loop will only carry on with the step if the condition is true.

This example of CHECK …

DO.
    " some code
    CHECK sy-index < 10.        
    " some code
ENDDO.

… is equivalent to …

DO.
    " some code
    IF sy-index >= 10.
        CONTINUE.
    ENDIF.
    " some code
ENDDO.