Program Logic and Design: AND and OR Operators

Combining AND and OR Operators

• Multiple AND conditions: Use when all conditions must be true.

  • Example: To pass a course, each of three test scores must be ≥ 75.
  • Declare constant MinScore = 75.
  • Comparison expression: Score1 ≥ 75 AND Score2 ≥ 75 AND Score3 ≥ 75.
  • Result: All three scores need to be ≥ 75 to pass.

• Multiple OR conditions: Use when any one condition must be true.

  • Example: To pass a course, at least one of three test scores must be ≥ 75.
  • Declare constant MinScore = 75.
  • Comparison expression: Score1 ≥ 75 OR Score2 ≥ 75 OR Score3 ≥ 75.
  • Result: If one score is ≥ 75, the evaluation short-circuits and the student passes.

Precedence in Combining AND and OR

• AND takes precedence over OR: In mixed expressions, AND conditions are evaluated first.

  • Example: For a discounted ticket, the expression Age ≥ 65 AND Rating = 'G' is evaluated before Age ≤ 12.

• Using Parentheses for Clarity:

  • Parentheses override default order of operations and improve clarity.
  • Example: (Age > 12 AND Age < 19) OR ValidID = 'Yes'.
  • Without parentheses: Pet = 'Dog' AND Age > 10 OR Age < 5.
  • With parentheses: Pet = 'Dog' AND (Age > 10 OR Age < 5).

Avoid Mixing AND and OR

• Nesting IF Statements: Preferred to avoid logic complexity.

  • Example: Nested IF for age checks and movie rating.
    • If Rating = 'G':
      • If Age ≤ 12 or Age ≥ 65, apply discount.
      • Else, no discount.

• Confidence with OR: If confident, use the OR operator in the first decision.

  • Example: Age ≤ 12 OR Age ≥ 65.
  • If true, apply discount; otherwise, proceed.

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That concludes the section on making decisions. Next topic: Loops.