Worksheet

F4.4 Decomposition and abstraction

Functions and structured code · GCSE · OCR J277 2.1.1, AQA 8525 3.1.1, Edexcel 1CP2 1.1.1 · about 20 min

What this lesson is about

Structure diagrams, and hiding the details of a job behind a function.

• Decomposition: breaking a problem down
• Abstraction: hiding the details
• Building from the bottom up, testing as you go

Questions 5 marks in all

1. [1 mark]What is decomposition?

   1. ABreaking a problem down into smaller, more manageable sub-problems
   2. BRemoving unnecessary detail
   3. CPutting code in alphabetical order
   4. DDeleting unused code

2. [1 mark]What is abstraction?

   1. ARemoving unnecessary detail to focus on what matters
   2. BBreaking a problem into parts
   3. CWriting code in capitals
   4. DTesting a program

3. [1 mark]A simulator's mat keeps the walls and distances but not the carpet colour. Which idea is that?

   1. AAbstraction
   2. BDecomposition
   3. CIteration
   4. DCasting

4. [1 mark]What does a structure diagram show?

   1. AA problem broken down into smaller sub-problems, top to bottom
   2. BThe order lines run in
   3. CThe values of variables as a program runs
   4. DHow data moves over a network

5. [1 mark]Why keep a delivery route as a list of stops, separate from the code that drives?

   1. AThe route can change without changing the functions
   2. BLists run faster than functions
   3. CPython requires it
   4. DFunctions cannot use numbers

The task: three stops

Write go_to(x, y) and signal(), then use them to visit three stops in order, signalling at each: A at (30, 10), B at (30, 60) and C at (0, 60), all in cm from where the robot starts. The robot starts in the bottom left of the mat.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

def go_to(x, y):
    """Drive to (x, y), in cm from where the robot started."""
    here_x, here_y = position()

def signal():
    """Light and beep at a stop."""
    led("green")

Plan your program here, then type it in and press Run.

Do it on the robot
www.bugbotlab.com/learn/f4-4-decomposition-and-abstraction/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. Add a fourth stop and a trip back to the start, by changing only the list of stops.
2. Draw a structure diagram for a robot that tidies balls into a box. Which boxes could reuse go_to?
3. Make go_to return how far it drove in total, and print the length of the whole route.