Good Learning Co.
SavannahYear 8
← Computing
ComputingAlgorithms and programming30 min★★★ difficulty

Breaking a program into functions

One long program is hard to fix. Six small functions are six small problems.

Part of your national curriculum
  • Algorithms and programming: Design and develop modular programs that use procedures or functions, and test and correct them systematically

Lesson overview

What you'll learn in this lesson

Design and develop modular programs that use procedures or functions, and test and correct them systematically

Key learning points

  • • Decomposition
  • • Parameters and return values
  • • Systematic testing

This lesson at a glance

  • 30 minutes
  • 13 parts to scroll through
  • 3 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

designmodularprogramsproceduresfunctions

Scroll down — the lesson carries on below

Part 1 of 13 · Discover8%
1

Watch & discover

Part 1 of 13

Watch first

Breaking a program into functions

An English teaching video on this topic from LearnFree. Watch it, then scroll down for the lesson.

In a nutshell

Design and develop modular programs that use procedures or functions, and test and correct them systematically

2

Learning cycle

Part 2 of 13

Learning cycle 1 of 2

Part 1 · Decomposition

A short piece of teaching, then a check to make sure it has landed.

3

Explore the idea

Part 3 of 13

Learn

Decomposition

Split the job into tasks that each do one thing: get input, validate it, calculate, display. Each becomes a function with a clear name.

4

Explore the idea

Part 4 of 13

Learn

Parameters and return values

Pass data in through parameters and hand the result back with a return, rather than relying on global variables. That makes each function testable on its own.

5

Quick check

Part 5 of 13

Quick check

What is decomposition?

6

Reset break

Part 6 of 13

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now
7

Quick check

Part 7 of 13

Quick check

Why prefer parameters over global variables?

8

Learning cycle

Part 8 of 13

Learning cycle 2 of 2

Part 2 · Systematic testing

A short piece of teaching, then a check to make sure it has landed.

9

Explore the idea

Part 9 of 13

Learn

Systematic testing

Test each function with normal, boundary and erroneous data. Fixing a bug inside one small function cannot break the rest of the program in the way an edit to a long script can.

10

Quick check

Part 10 of 13

Quick check

Which three types of test data should you use?

11

Challenge round

Part 11 of 13

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

12

Mastery quiz

Part 12 of 13

Marked quiz

End of lesson quiz: Breaking a program into functions

3 questions, marked with the reasoning shown. No timer.

  1. 1. What is decomposition?

  2. 2. Why prefer parameters over global variables?

  3. 3. Which three types of test data should you use?

13

Lesson round-up

Part 13 of 13

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 3 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Article

How a supermarket checkout knows the price

When a barcode is scanned, the checkout does not store the price itself. It sends the barcode number to a database and reads back a record: product name, price, whether it needs an age check. The record is the single place the price lives, so changing one row changes every till in the shop at once.

Problems come from bad data, not bad scanners. If two products share a barcode, or a price update reaches the shop overnight but the till holds an old copy in its cache, customers are charged the wrong amount. Shops check this with test transactions: scan a known item, expect a known price, record what actually happened.

Good systems also log every scan. If a customer complains, the log shows exactly which record was used and when.

Written for Good Learning Co.

Reading questions

  1. Write in your own words what the checkout sends and what it receives back.
  2. Explain one way bad data could cause a wrong price, and how logging helps find it.
  3. Design a test table with four tests for a new checkout, with expected and actual results.

  • Reading and notes

    Reading

    Read the lesson text again and note the key terms and how each one is used, in your own words — as you would for revision.

    Half a page of notes

  • Extended writing

    Writing

    Explain a real system that uses this idea — how it works, where it can go wrong, and how you would make it safer or better.

    250–350 words

  • Algorithm on paper

    Diagram

    Write your steps out as pseudocode or a flowchart before you type anything, then photograph it.

    1 flowchart or 10 lines

  • Code write-up

    Writing

    Copy your code in, then explain underneath what each part does and what you had to fix.

    Code + 5 sentences

  • Test table

    Working out

    Make a test table: what you tried, what you expected, what actually happened.

    4–6 tests

Saved as you type.

Part 1 of 13 · Watch & discover

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    Design and develop modular programs that use procedures or functions, and test and correct them systematically

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