Write algorithms with decision-making (branching, looping)

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 instructions in order to get a tasty dish. In computing, the recipe is written in plain language or a diagram.

Key properties:

• Well‑defined steps
• Finite number of steps
• Input and output
• Deterministic (same input gives same output)

Flowcharts – Visualising Algorithms

Flowcharts use shapes to represent actions:

• Oval – Start/End
• Rectangle – Process/Instruction
• Diamond – Decision (branch)
• Parallelogram – Input/Output

Example: Check if a number is even or odd

1. Start
2. Input number $n$
3. Decision: Is $n \bmod 2 = 0$?
4. If yes → Output “Even”
5. If no → Output “Odd”
6. End

🧩 Flowcharts help you spot errors before coding.

Decision-Making (Branching)

Branching lets the algorithm choose a path based on a condition.

Syntax in pseudocode:

IF condition THEN
    // do something
ELSE
    // do something else
END IF

Example: Grade a test

1. Input score $s$
2. IF $s \ge 90$ THEN Grade = A
3. ELSE IF $s \ge 80$ THEN Grade = B
4. ELSE IF $s \ge 70$ THEN Grade = C
5. ELSE Grade = F

🔀 Remember: each IF can have an ELSE IF or ELSE.

Looping (Repetition)

Loops repeat a block of code while a condition holds.

Common loop types:

• FOR – fixed number of iterations
• WHILE – until condition is false
• DO‑WHILE – execute at least once

Example: Sum the first 10 natural numbers

sum = 0
FOR i = 1 TO 10
    sum = sum + i
END FOR
// sum = 55

🔄 Loops are like a conveyor belt that keeps moving items until a stop signal.

Putting It All Together – A Mini‑Project

Write an algorithm to find the largest of three numbers.

1. Start
2. Input $a$, $b$, $c$
3. Set $max = a$
4. IF $b > max$ THEN $max = b$
5. IF $c > max$ THEN $max = c$
6. Output $max$
7. End

🛠️ Test with different inputs to ensure it works.

Exam Tips

📚 Practice by writing algorithms for everyday tasks – like making a sandwich or planning a school trip. The more you practice, the easier it becomes!