ABAP IF Statement: Conditional Program Flow Control

Syntax

The IF statement comes in various forms:

1. Simple `IF` Condition (without Alternative)

IF <logical_expression>.
  " Statement block 1
  " This block is only executed if <logical_expression> is true.
  [Statement1_1].
  [Statement1_2].
  ...
ENDIF.

IF: Initiates the condition check.
<logical_expression>: A condition that evaluates to true (abap_true) or false (abap_false).
ENDIF: Closes the IF block.

2. `IF` Condition with Alternative (`ELSE`)

IF <logical_expression>.
  " Statement block 1 (If true)
  ...
ELSE.
  " Statement block 2 (If false)
  ...
ENDIF.

ELSE: Initiates the block that is executed if the <logical_expression> in the IF part was false.

3. `IF` Condition with Multiple Alternatives (`ELSEIF`) and Optional `ELSE`

IF <logical_expression_1>.
  " Statement block 1 (If expression 1 is true)
  ...
ELSEIF <logical_expression_2>.
  " Statement block 2 (If expression 1 was false AND expression 2 is true)
  ...
ELSEIF <logical_expression_3>.
  " Statement block 3 (If expressions 1 & 2 were false AND expression 3 is true)
  ...
[ELSE. " Optional block for all other cases
  " Statement block N (If ALL previous expressions were false)
  ...]
ENDIF.

ELSEIF: Checks another condition, but only if all previous IF and ELSEIF conditions were false.

Functionality and Flow

Conditions are checked strictly from top to bottom (IF first, then the first ELSEIF, then the second, etc.).
As soon as a condition is recognized as true (abap_true), the associated statement block is executed.
Very important: After executing this one block, the program jumps directly to the statement after ENDIF. No further ELSEIF conditions or the ELSE block within the same IF...ENDIF structure are checked or executed.
If all IF and ELSEIF conditions are false (abap_false), the ELSE block is executed (if present).
If all conditions are false and there is no ELSE block, execution simply continues with the statement after ENDIF, without executing any of the blocks within the IF structure.

Logical Expressions

The <logical_expression> can take various forms:

Comparisons: =, <>, <, >, <=, >= (e.g., count > 0, text = 'Yes')
State checks: var IS INITIAL, ref_var IS BOUND
Boolean variables: is_ok = abap_true
Logical operators for combination:
- AND: Both sub-expressions must be true.
- OR: At least one of the sub-expressions must be true.
- NOT: Reverses the result of the following expression.
- Example: IF count > 0 AND is_active = abap_true.
Predicate functions: Functions that return abap_true or abap_false (e.g., line_exists(...)).

Nesting

IF statements can be nested within each other to build more complex decision trees. Good indentation is essential for readability here.

IF condition1.
  IF condition2.
    " ... "
  ENDIF.
ELSE.
  " ... "
ENDIF.

Examples

1. Simple IF

DATA quantity TYPE i VALUE 15.

IF quantity > 10.
  WRITE / 'Order quantity is greater than 10.'.
ENDIF.

2. IF with ELSE

DATA user_input TYPE c LENGTH 1.
user_input = 'X'. " Example input

IF user_input = 'Y'.
  WRITE / 'User said Yes.'.
ELSE.
  WRITE / 'User did not say Yes.'.
ENDIF.

3. IF with ELSEIF and ELSE

DATA score TYPE i VALUE 75.
DATA grade TYPE c LENGTH 1.

IF score >= 90.
  grade = 'A'.
ELSEIF score >= 70.
  grade = 'B'.
ELSEIF score >= 50.
  grade = 'C'.
ELSE.
  grade = 'D'.
ENDIF.

WRITE / 'The grade is:', grade. " Output: The grade is: B

4. Combined Condition (AND)

DATA has_permission TYPE abap_bool VALUE abap_true.
DATA is_logged_in TYPE abap_bool VALUE abap_true.

IF has_permission = abap_true AND is_logged_in = abap_true.
  WRITE / 'Access granted.'.
ELSE.
  WRITE / 'Access denied.'.
ENDIF.

Distinction from `CASE`

When you want to check the same variable against multiple different, fixed values, the CASE statement is often clearer than a long chain of IF ... ELSEIF statements:

DATA transport TYPE c LENGTH 1. " B=Bike, C=Car, T=Train

transport = 'C'.

" With IF/ELSEIF
IF transport = 'B'.
  WRITE / 'Bike selected.'.
ELSEIF transport = 'C'.
  WRITE / 'Car selected.'.
ELSEIF transport = 'T'.
  WRITE / 'Train selected.'.
ELSE.
  WRITE / 'Unknown.'.
ENDIF.

" With CASE (often more readable)
CASE transport.
  WHEN 'B'.
    WRITE / 'Bike selected.'.
  WHEN 'C'.
    WRITE / 'Car selected.'.
  WHEN 'T'.
    WRITE / 'Train selected.'.
  WHEN OTHERS.
    WRITE / 'Unknown.'.
ENDCASE.

Important Notes / Best Practice

The IF statement is fundamental to almost every ABAP program.
Pay attention to clear and unambiguous logical expressions.
Use indentation consistently to make the structure readable.
Never forget the closing ENDIF.
For purely value-based assignments, modern ABAP (>= 7.40) often offers more compact alternatives like the conditional operators COND and SWITCH. However, IF remains essential for controlling statement blocks.