Draw a flowchart from a structured English description

9.2 Algorithms – Drawing Flowcharts from Structured English

What is Structured English?

Structured English is a plain‑English style that uses a limited set of keywords (IF, THEN, ELSE, END IF, WHILE, END WHILE, etc.) to describe the logic of an algorithm. It’s like writing a recipe that a computer can follow, but still readable by humans. 🎂

Why Use Flowcharts?

Flowcharts turn those sentences into visual symbols, making the flow of control easier to spot. Think of a flowchart as a map of a city: streets (arrows) show the path, and buildings (shapes) tell you what happens at each stop. 🗺️

Common Flowchart Symbols

Step‑by‑Step: From English to Flowchart

1. Read the description carefully. Highlight keywords: IF, THEN, ELSE, WHILE, END, etc.
2. Identify the start and end points. Place an oval for BEGIN and another for END.
3. Break the description into atomic actions. Each action becomes a rectangle.
4. Locate decisions. Anything that checks a condition becomes a diamond.
5. Connect the shapes with arrows. Show the flow from one step to the next.
6. Check loops. A WHILE loop will have an arrow that goes back to the decision diamond.
7. Validate. Walk through the flowchart with a sample input to ensure it matches the description.

Illustrative Example

Structured English:

BEGIN
  INPUT number
  IF number MOD 2 = 0 THEN
    SET result = number + 2
  ELSE
    SET result = number - 1
  END IF
  OUTPUT result
END

[🟢 BEGIN]
   |
   v
[🟦 INPUT number]
   |
   v
[🔺 number MOD 2 = 0?]
   |          \
   |           \
   v            v
[🟦 result = number + 2]   [🟦 result = number - 1]

   +-----------+--------------+
               |
               v
[🟦 OUTPUT result]
   |
   v
[🟢 END]

Practice Exercise

Write a flowchart for the following structured English. Try to draw it on paper or using a diagram tool. Then compare with the solution below.

BEGIN
  INPUT age
  IF age < 18 THEN
    OUTPUT "Underage"
  ELSE IF age < 65 THEN
    OUTPUT "Adult"
  ELSE
    OUTPUT "Senior"
  END IF
END

Solution

Flowchart (text version):

[🟢 BEGIN]
   |
   v
[🟦 INPUT age]
   |
   v
[🔺 age < 18?]
   |          \
   |           \
   v            v
[🟦 OUTPUT "Underage"]   [🔺 age < 65?]
   |                          |          \
   +-----------+--------------+           \
               |                          v
               |                [🟦 OUTPUT "Adult"]

               +--------------------------+
                                      |
                                      v
                               [🟦 OUTPUT "Senior"]
                                      |
                                      v
                               [🟢 END]

Key Takeaways

• Structured English uses a fixed set of keywords that map directly to flowchart symbols.
• Start with the BEGIN/END ovals, then add rectangles for actions, diamonds for decisions, and arrows for flow.
• Loops (WHILE) are represented by a decision diamond with an arrow looping back.
• Always test your flowchart with sample data to confirm it behaves as described.
• Practice by converting short descriptions into flowcharts; the more you do, the faster you’ll spot patterns.

Further Resources

- Cambridge A‑Level CS 9618 Study Guide (Chapter 9) - Online flowchart makers: draw.io, Lucidchart - Practice problems on the Cambridge Assessment website