Selection and Iteration

Selection — IF statements

IF score >= 70 THEN
    OUTPUT "Distinction"
ELSEIF score >= 50 THEN
    OUTPUT "Pass"
ELSE
    OUTPUT "Fail"
ENDIF

Nested IF & logical operators

IF age >= 13 AND age <= 19 THEN
    OUTPUT "Teenager"
ENDIF

Iteration — loops

Count-controlled (FOR) — known number of repeats:

FOR i ← 1 TO 10
    OUTPUT i
NEXT i

Condition-controlled (WHILE) — repeats while true, may run zero times:

WHILE password != "1234"
    password ← INPUT
ENDWHILE

REPEAT…UNTIL — runs at least once, checks at the end:

REPEAT
    num ← INPUT
UNTIL num > 0

Choosing a loop

• Know how many times? → FOR
• Depends on a condition / input? → WHILE or REPEAT

Exam tip

A WHILE loop checks the condition first (could run 0 times); REPEAT checks last (always runs ≥1 time). State this difference for marks.