Cambridge Syllabus Notes

🔍 Algorithm Design & Problem‑Solving – Cambridge IGCSE 0478

What is an Algorithm?

An algorithm is a step‑by‑step recipe that solves a problem or performs a task. Think of it like a cooking recipe: you follow the steps in order to get a tasty dish.

🗺️ Flowcharts

Why Use Flowcharts?

Flowcharts give a visual map of the algorithm. They help you spot mistakes before you write code.

🔹 Common Symbols:

🟢 Oval – Start/End
🟦 Rectangle – Process/Action
🔺 Diamond – Decision (Yes/No)
➡️ Arrow – Flow of control

🔹 Example: Find the Largest of Three Numbers

Step	Flowchart Symbol	Description
1	🟢 Start	Begin algorithm
2	🟦 Input a, b, c	Read three numbers
3	🔺 a > b?	Is a greater than b?
4	➡️ Yes → 🔺 a > c?	If a > b, check a > c
5	➡️ Yes → 🟦 Largest = a	a is largest
6	➡️ No → 🟦 Largest = c	c is largest
7	➡️ No → 🟦 Largest = b	b is largest
8	🟢 End	Finish algorithm

🧩 Structure Diagrams

What Are Structure Diagrams?

Structure diagrams show the hierarchy and relationships between different parts of an algorithm. They’re like a family tree for your code.

🔹 Example: Calculating the Average of Five Scores

Component	Description
Input Module	Collects five scores from the user.
Processing Module	Adds the scores and divides by 5.
Output Module	Displays the average.

✍️ Pseudocode

Why Pseudocode?

Pseudocode lets you write the algorithm in plain English (or your native language) without worrying about syntax. It’s the bridge between the flowchart and the actual code.

🔹 Example: Calculating the Largest of Three Numbers (Pseudocode)

START
  INPUT a, b, c
  IF a > b THEN
    IF a > c THEN
      largest ← a
    ELSE
      largest ← c
    END IF
  ELSE
    IF b > c THEN
      largest ← b
    ELSE
      largest ← c
    END IF
  END IF
  OUTPUT largest
END

📚 Exam Tips & Tricks

1️⃣ Understand the Question

Read the problem carefully. Highlight keywords like “calculate”, “compare”, “loop”, and “output”.

2️⃣ Sketch a Flowchart First

Even a rough sketch helps you organise your thoughts and spot missing steps.

3️⃣ Use Clear Variable Names

Names like maxValue or totalScore make your pseudocode easier to read.

4️⃣ Check Edge Cases

What happens if two numbers are equal? Think about all possible inputs.

5️⃣ Practice, Practice, Practice

Try different problems: sorting lists, calculating factorials, or simulating a simple game.

🚀 Final Thought

Remember, an algorithm is like a well‑planned road trip: you need a map (flowchart), a route plan (structure diagram), and a travel guide (pseudocode) to reach your destination (the correct answer) smoothly. Keep practicing, and soon you’ll design algorithms as naturally as you write sentences!

Use flowcharts, structure diagrams and pseudocode to construct a solution