Use pseudocode to write: an 'IF' statement including the 'ELSE' clause and nested IF statements

Topic 11.2 – Constructs

Learning Objective

Write pseudocode that demonstrates:

• An IF statement with an ELSE clause.
• Nested IF statements.

1. Basic IF‑ELSE Structure

The general form of an IF‑ELSE statement in pseudocode is:

Example – deciding whether a student passes:

• IF \$mark \ge 40\$ THEN
•    output “Pass”
• ELSE
•    output “Fail”
• END IF

2. Nested IF Statements

When a decision depends on more than one condition, an IF can be placed inside another IF block. The syntax remains the same; the inner IF is simply indented for readability.

General pattern:

• IF outer‑condition THEN
•    IF inner‑condition THEN
•       … statements …
•    ELSE
•       … statements …
•    END IF
• ELSE
•    … statements …
• END IF

Example – grading a test based on two criteria:

• IF \$score \ge 70\$ THEN
•    output “Distinction”
• ELSE
•    IF \$score \ge 50\$ THEN
•       output “Merit”
•    ELSE
•       output “Pass”
•    END IF
• END IF

3. Common Pitfalls

1. Forgetting the END IF – leads to ambiguous block termination.
2. Using assignment (=) instead of comparison (= = or ≠) in the condition.
3. Mixing indentation levels, which makes the logic hard to follow.
4. Placing an ELSE without a preceding IF block.

4. Practice Exercise

Write pseudocode to determine the shipping cost for an online order. The rules are:

• If the order total is at least \$£100\$, shipping is free.
• Otherwise, if the customer is a “Premium” member, shipping costs £5.
• Otherwise, shipping costs £10.

Include both an IF‑ELSE version and a nested IF version.