Logic: AND, OR, NOT

A club that checks both ends of the age

• A club takes members only from 11 to 16. One test cannot say both ends.
• AND is TRUE only when both tests are TRUE: Age >= 11 AND Age <= 16.
• NOT flips a Boolean. The tasks use it on a flag, not on a number.

DECLARE Age : INTEGER
Age ← 14
IF Age >= 11 AND Age <= 16 THEN
    OUTPUT "accepted"
ELSE
    OUTPUT "no"
ENDIF

A fare that depends on either age

• A bus fare is free under 5, or at 65 and over. One of those tests is enough.
• OR is TRUE when either operand is TRUE.

DECLARE Age : INTEGER
Age ← 70
IF Age < 5 OR Age >= 65 THEN
    OUTPUT "free"
ELSE
    OUTPUT "pay"
ENDIF

Nest the second decision

• 80 or more is a distinction. Otherwise, 50 or more is a pass, and the rest is a fail.
• The second IF is the statement under ELSE, with its own ENDIF.
• THEN stays on the IF line, including the inner one.

DECLARE Mark : INTEGER
Mark ← 72
IF Mark >= 80 THEN
    OUTPUT "Distinction"
ELSE
    IF Mark >= 50 THEN
        OUTPUT "Pass"
    ELSE
        OUTPUT "Fail"
    ENDIF
ENDIF

Watch out

• Write the variable on both sides of AND. Mark >= 0 AND <= 100 is not a test.
• IGCSE 0478 puts THEN on the following line. Do not mix the two papers.

Common mistakes

• ELSE belongs to the IF above it. Indent the inner IF so the final ENDIF is the outer one.
• NOT applies to a Boolean. NOT Mark is not how you test a number.

Now you try

• One task is an OR, one is a NOT, and one is the nested grade.