Logic: AND, OR, NOT

A club that checks your age

• A coding club takes members only from age 11 to 16. One test cannot say both ends.
• AND is TRUE only when both tests are TRUE.
• Write the variable on each side: Age >= 11 AND Age <= 16.

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

OR: either test is enough

• A bus fare is free for a child or a senior: under 5, or 65 and over.
• OR is TRUE when at least one test is TRUE.

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

NOT flips a Boolean

• NOT turns TRUE into FALSE, and FALSE into TRUE.
• A search that has not found the target yet is NOT Found.

DECLARE Found : BOOLEAN
Found ← FALSE
IF NOT Found
  THEN
    OUTPUT "missing"
ENDIF

Watch out

• Mark >= 0 AND <= 100 is not a test. The second half has nothing to compare.
• Parentheses make a mix obvious: NOT (Age < 11 OR Age > 16).

Common mistakes

• AND, OR and NOT are keywords. Their operands are BOOLEAN, usually from a relational test.
• 9618 puts THEN on the IF line. This course keeps THEN on the next line.

Now you try

• Each task is one decision. Write both sides of AND and of OR.
• Press Check answer to test it.