ABAP Core Part 4: Control Flow and Building Output Texts

📌 KEY POINTS
✅ Branches: IF/ELSEIF/ELSE and CASE/WHEN/WHEN OTHERS.
✅ Loops: LOOP AT itab (tables), DO n TIMES, WHILE condition; leave with EXIT, skip with CONTINUE or CHECK.
✅ Texts are built with CONCATENATE … INTO … SEPARATED BY space, formatted with WRITE … TO and cleaned with CONDENSE.
⚠️ CHECK inside a loop skips to the next iteration; outside a loop it leaves the processing block.

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▶ WHERE WE ARE
Parts 2–3 declared data. Now the program makes decisions, repeats work and produces readable text.

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▶ 1. IF AND CASE
IF lv_free = 0. … ELSEIF lv_free < 10. … ELSE. … ENDIF.
Comparison: =, <>, <, >, <=, >=, BETWEEN, IN (ranges), IS INITIAL, IS NOT INITIAL.
Logical: AND, OR, NOT — use parentheses for clarity.
CASE lv_carrid. WHEN 'LH'. … WHEN 'AA' OR 'UA'. … WHEN OTHERS. … ENDCASE.

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▶ 2. LOOPS

• LOOP AT lt_flights INTO ls_flight WHERE carrid = 'LH'. … ENDLOOP. — main loop for internal tables (details in Internal Tables).
• DO 5 TIMES. … ENDDO. — fixed repetitions; sy-index is the counter.
• WHILE lv_x < 100. … ENDWHILE. — condition-based.
• EXIT leaves the loop; CONTINUE jumps to the next iteration; CHECK cond skips the iteration if cond is false.

⚠️ DO without TIMES needs an EXIT, otherwise it never ends.

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▶ 3. BUILDING TEXTS

• CONCATENATE lv_a lv_b INTO lv_text SEPARATED BY space.
• WRITE lv_date TO lv_char (user date format), WRITE lv_amount TO lv_char CURRENCY lv_waers.
• CONDENSE lv_text — remove extra blanks; SHIFT, TRANSLATE … TO UPPER CASE.
• Leading zeros: CONVERSION_EXIT_ALPHA_OUTPUT (e.g. connection 0400 → 400).

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▶ 4. MODERN SYNTAX (SIDE NOTE)
From 7.40: COND/SWITCH assign values by condition in one expression, and string templates |Flight { lv_connid }| replace CONCATENATE. Useful to read in newer code; the classic statements do the same job.

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▶ STEP BY STEP

1. Loop over flights of an airline and skip past dates with CONTINUE.
2. Classify each flight with IF/ELSEIF into FULL / ALMOST FULL / AVAILABLE.
3. Build an output line with WRITE … TO and CONCATENATE.
4. React per status with CASE.

✅ CHECKPOINT: you can branch, loop and produce readable text with classic statements.

A billing report built its output lines with nested CONCATENATE statements and manual date formatting ("DD.MM.YYYY" built with offsets). When the company rolled the report out to US users, dates appeared in the wrong format and amounts had the wrong decimals for JPY.
Replacing the code with string templates using DATE = USER and CURRENCY = currency fixed both issues without special handling per country, and halved the code size.

• DO loops without EXIT.
• Long IF chains where COND or CASE is clearer.
• Formatting dates and amounts manually with offsets.
• Using CHECK outside loops without knowing it leaves the block.
• Forgetting WHEN OTHERS in CASE.

• Use COND/SWITCH for value assignments, IF/CASE for actions.
• Keep loop bodies short; move logic into methods.
• Use string templates with formatting options.
• Always provide an exit condition.
• Use WHERE in LOOP AT instead of IF inside the loop when possible.

Questions: "Difference between CONTINUE, EXIT and CHECK?", "What are COND and SWITCH?", "How do string templates format dates and currencies?"
Strong answer: CONTINUE skips to the next iteration, EXIT leaves the loop, CHECK skips when false (inside loops) or leaves the block; COND evaluates conditions, SWITCH compares one operand, both return values; templates embed expressions in { } with options like DATE = USER, CURRENCY =, ALPHA = OUT, and && chaining.