2.2 · Flowcharts

Goal: read and draw flowcharts using the standard symbols.

Standard symbols

Symbol	Shape	Use
Terminator	Rounded rectangle / oval	Start, End
Process	Rectangle	An action (assignment, computation)
Input / Output	Parallelogram	Reading from / writing to the user
Decision	Diamond	A yes/no question
Flow line	Arrow	Direction of execution
Connector	Small circle	Continues elsewhere (avoid line crossings)
Subroutine call	Rectangle with double vertical bars	Call to another subroutine

Example · BMI category flowchart

            ┌────────────┐
            │  Start     │
            └────┬───────┘
                 │
            ┌────▼────────────┐
            │ Input weight, h │
            └────┬────────────┘
                 │
            ┌────▼─────────┐
            │ bmi ← w/h²   │
            └────┬─────────┘
                 │
              ◇──┴──◇  YES   ┌──────────────┐
              ◇bmi<18.5◇──▶  │Output "Under"│
              ◇──┬──◇         └────┬─────────┘
                 │ NO               │
              ◇──┴──◇  YES   ┌──────────────┐
              ◇bmi<24◇──▶    │Output "Norm" │
              ◇──┬──◇         └────┬─────────┘
                 │ NO               │
              ┌──┴──────────────┐   │
              │Output "Over/Obese"│ │
              └────┬─────────────┘ │
                   └──────┬────────┘
                          ▼
                     ┌────────┐
                     │   End  │
                     └────────┘

(The HKEAA reproduces flowcharts in their nicer printed form — but the symbol set is identical.)

Rules of good flowcharts

• One entry, one exit per process.
• Flow lines should not cross (use connectors).
• Decision diamonds must have exactly one YES and one NO branch.
• Keep nesting under 3 levels — if deeper, decompose into sub-flowcharts.

When to use a flowchart vs pseudocode

Use flowcharts when	Use pseudocode when
Audience prefers visual	Audience can read code-style
Showing branching logic	Showing detailed step sequence
SBA design documents	Coding implementation notes

Exam-style question

Q (5 marks): Draw a flowchart that reads a student's mark and outputs "Pass" if ≥ 50 and "Fail" otherwise.

Sample answer (text representation):

1. Start.
2. Input mark.
3. Decision: mark ≥ 50?
   • YES → Output "Pass" → End.
   • NO → Output "Fail" → End.

In the exam draw the actual shapes — terminator, parallelogram for input, diamond for decision, parallelograms for outputs, terminators for End.

Key takeaways

• Five symbols cover almost everything.
• One entry / one exit; no crossing lines.
• Pair flowcharts with pseudocode for clarity.

➡️ Next: 2.3 Data Types & Structures