IGCSE · Practice questions · Decomposition, structure diagrams, flowcharts and pseudocode

Draw the plan.

Six original Cambridge-style questions on decomposition, structure diagrams, flowcharts and pseudocode.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

What, then how.

Decompose: inputs, processes, outputs, storage.
Structure diagram: the hierarchy of sub-systems; no order or decisions.
Flowchart: terminator, process, input/output, decision, subroutine, flow lines.
Purpose: say what the algorithm is for in its context, then describe the processes.

Recall

[4 marks]

Draw and name the flowchart symbols used for: (a) the start of a flowchart; (b) Total ← Total + Price; (c) OUTPUT Total; (d) Price > 100?

(a) Terminator: rounded rectangle. ✓
(b) Process: rectangle. ✓
(c) Input/output: parallelogram. ✓
(d) Decision: diamond (with two labelled exits). ✓

Apply

[4 marks]

A smart thermostat keeps a room at a temperature chosen by the user. Identify one input, one process, one output and one item of storage.

Input: the temperature from the sensor (or the temperature chosen by the user). ✓
Process: compare the room temperature with the chosen temperature. ✓
Output: switch the heater on or off (or show the temperature on a display). ✓
Storage: the chosen (target) temperature. ✓

Apply

[3 marks]

A program for a school canteen lets students order lunch. Draw a structure diagram with the top-level box "Canteen ordering" and three sub-systems below it.

Top box "Canteen ordering" joined by lines to the boxes below it. ✓
Three sensible sub-systems, e.g. Log in, Choose meal, Pay. ✓
Drawn as a hierarchy (boxes and lines, no arrows or decisions). ✓

Explain

[2 marks]

State the purpose of this algorithm.

Total ← 0
FOR Day ← 1 TO 7
    INPUT Steps
    Total ← Total + Steps
NEXT Day
OUTPUT Total

It inputs the number of steps walked on each of 7 days. ✓
It adds them up and outputs the total number of steps for the week. ✓

Explain

[2 marks]

Explain one difference between a structure diagram and a flowchart.

A structure diagram shows how a system is decomposed into sub-systems (a hierarchy). ✓
A flowchart shows the order of the steps of an algorithm, including decisions and loops. ✓

Analysis

[2 marks]

A student draws a flowchart in which a decision diamond Age >= 18? has only one line coming out of it. Explain the error and how to correct it.

A decision must have two exits, one for each outcome. ✓
Add a second flow line and label the two exits Yes and No (True and False). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.