← IGCSE Computer Science Paper 2

Choosing a design method: structure diagram, flowchart or pseudocode

Shows the parts of a solution as boxes. Flowcharts (pictures) and pseudocode (text) then show the steps of each box in order. Draw the structure diagram first.

Part of: IGCSE Computer Science 0478 — 7b Decomposition and Sub-systems — Module 25, WA Computer Science ATAR Year 11 — Pseudocode and Algorithm Design — Module 14

Understanding Choosing a design method: structure diagram, flowchart or pseudocode in IGCSE Computer Science Paper 2

What it does: This is pseudocode: capitalised keywords and an indented loop body show the steps in text, close to a real program. The main problem sits at the top and is split into boxes for each part. Each box then gets its own flowchart or pseudocode. A structure diagram shows WHAT the parts of the solution are. A flowchart shows the order of steps inside one part.

Common mistakes: The block ends with ENDPROCEDURE, so it must start with PROCEDURE ShowMenu(). A subroutine that only outputs and returns no value is a procedure, not a function. In Cambridge pseudocode, assignment uses the arrow ←, not =. The line should be Total ← Maths + English.

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This module's key terms are also in a printable crossword (Modules 107–118) and word search (Modules 94–118).

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Learning
Duo
Which method shows a solution broken down into its parts (sub-systems) as boxes?
Structure diagramFlowchart
Matches
Use a structure diagram to show the exact order of each step inside a loop
↓
A structure diagram shows the parts of a solution, not the order of steps. A flowchart or pseudocode shows the steps in order.
Applying
Meanings
Term
structure diagram
Meaning
Shows the parts of a solution as boxes. Flowcharts (pictures) and pseudocode (text) then show the steps of each box in order. Draw the structure diagram first.
Practice
// Main program: one CALL per box
Testing
Gaps
ShowResult()
Check Answer
Spots
1FUNCTION ShowMenu()
2 OUTPUT "Menu"

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Quick Questions

1. Which method shows a solution broken down into its parts (sub-systems) as boxes?
A. Structure diagram ✓
B. Flowchart
A structure diagram shows WHAT the parts of the solution are. A flowchart shows the order of steps inside one part.
2. Which method draws the steps of an algorithm as a picture using symbols and arrows?
A. Structure diagram
B. Flowchart ✓
Flowcharts use Cambridge symbols joined by arrows to show the steps in order. A structure diagram does not show step order.
3. Which method writes the steps of an algorithm as text that looks close to real code?
A. Pseudocode ✓
B. Structure diagram
Pseudocode uses keywords like IF, FOR and OUTPUT in capitals, so it is easy to turn into a real program.
4. A school system has parts called Login, Marks and Reports. Which method do you use FIRST?
A. Pseudocode
B. Structure diagram ✓
Decompose the problem first. Draw the structure diagram, then write an algorithm for each box.
5. You have a structure diagram with a box called Calculate Total. What do you do next for that box?
A. Write an algorithm for it as a flowchart or pseudocode ✓
B. Draw another structure diagram of the whole system
Each box needs an algorithm showing its steps in order. A flowchart or pseudocode can do this.

Match the Pairs

Structure diagram → Shows the parts of a solution as boxes, split from the main problem into sub-problems. Draw it first.
Flowchart → A picture of the steps of an algorithm in order, using shapes joined by arrows.
Pseudocode is a text-based method that reads close to real code, so it shows the steps of an algorithm in order → FOR Count ← 1 TO 5 OUTPUT Count NEXT Count
A structure diagram splits a program into sub-problems, so each box can then be given its own algorithm → Quiz Program -> Ask Question | Mark Answer | Show Score
Use a structure diagram to show the exact order of each step inside a loop → A structure diagram shows the parts of a solution, not the order of steps. A flowchart or pseudocode shows the steps in order.
Write the pseudocode for every box first, then draw the structure diagram last → The order is wrong. The structure diagram must be drawn first to find the parts, then an algorithm is written for each box.

Key Term

structure diagram
Shows the parts of a solution as boxes. Flowcharts (pictures) and pseudocode (text) then show the steps of each box in order. Draw the structure diagram first.

Fill in the Blanks

1. PROCEDURE ShowResult() OUTPUT "Well done" ENDPROCEDURE
Hint: Type the keyword that starts the pseudocode for one box of the structure diagram.
2. CALL GetMarks() CALL CalcTotal() CALL ShowTotal()
Hint: Type the keyword the main program uses to run a procedure, one for each box.
3. Total ← Mark1 + Mark2 Average ← Total / 2 OUTPUT Average
Hint: Type the assignment symbol used in Cambridge pseudocode to store a value in a variable.
4. IF Mark >= 50 THEN OUTPUT "Pass" ENDIF
Hint: Type the keyword that follows the condition and matches the decision diamond in a flowchart.
5. FOR Count ← 1 TO 5 OUTPUT Count NEXT Count
Hint: Type the keyword that sits between the start value and end value of a counted loop.

Spot the Error

Question 1
A FUNCTION ShowMenu()
B OUTPUT "Menu"
C ENDPROCEDURE
Line A — The block ends with ENDPROCEDURE, so it must start with PROCEDURE ShowMenu(). A subroutine that only outputs and returns no value is a procedure, not a function.
Question 2
A PROCEDURE GetMarks()
B INPUT Maths
C INPUT English
D Total = Maths + English
E ENDPROCEDURE
Line D — In Cambridge pseudocode, assignment uses the arrow ←, not =. The line should be Total ← Maths + English.
Question 3
A INPUT Name
B INPUT Score
C PRINT Name, Score
Line C — Cambridge pseudocode uses the keyword OUTPUT to display values, not PRINT. The line should be OUTPUT Name, Score.
Question 4
A FOR Count ← 1 UNTIL 5
B OUTPUT Count
C NEXT Count
Line A — A FOR loop sets its range with TO. UNTIL belongs to REPEAT loops. The line should be FOR Count ← 1 TO 5.
Question 5
A INPUT Age
B OUTPUT "Checking age"
C IF Age ← 16 THEN
D OUTPUT "Can apply"
E ENDIF
Line C — The condition must compare values, not assign one. It should be IF Age >= 16 THEN. The arrow ← is only for assignment.

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