4 – Break Down a Problem

• Develop problem solving skills by decomposition
• Learn how to represent algorithms using flowcharts
• Learn how to represent algorithms using pseudo-code
• Understand how abstraction can help solving complex problems
• Develop further understanding that programming bridges the gap between algorithmic solutions and computers

• decomposition
• algorithms

• flowcharts
• pseudo-code

• abstraction
• selection

• Sometimes, the problem is complex or seemingly complex. A common approach to solve a complex problem is to break down the problem into smaller, easier to solve problems. After we solved each of those smaller problems, the complex problem is solved.
• The above approach to problem solving is called divide-and-conquer.
• In computer science, to breaking down a problem into smaller, easier to solve problems is called decomposition.
• Let’s try decomposition on the following not so complex problem:

 Write a program such that when a user inputs a number, the program will output it is an even or an odd number.

• To break down the above problem, we are going to use flowchart to help us.
• Flowcharts are very useful in visualising how algorithms work.

• A flowchart is a type of diagram that represents an algorithm, workflow or process, showing the steps as boxes of various kinds, and their order by connecting them with arrows.
• Each shape represent some steps in the algorithm:

• The following is a simple example of using flowchart to describe the steps to a simple problem of determining if an user’s input numbers are odd or not.

• The above problem has been decomposed into three parts:
  1. a user input a number
  2. determine if the number is even or odd
  3. output the appropriate message depending on the above step

Try It

Write a computer game that allows a user to guess the number that is
 picked by a computer. If the user guessed the number, the user is 
declared a winner. If the user guessed incorrectly, the computer will
 tell the user if the guess is too high or two low. 

• Try your decomposition skill with the above problem.
• The first few steps have been started for you:
  1. computer pick a number
  2. a user input a number

• Finish decomposing the problem by finishing all steps required to reach a solution.
• Create a flowchart using appropriate symbols for your steps.
• Upload both your steps and flowchart to www.bournetolearn.com.

• Launch the application Flowol, click on File->New and you should see something like the following:

• Select the lighthouse mimic by clicking on it
• The scenario or mimic has one input:the Sun and three outputs: Lamp, Lights and Foghorn

Try It

• Flowol is simple to use once you know it
• See if you can work out how to create a flowchart as shown below:

• If you get stuck, ask your teacher to show you.

• The above flowchart will make the three outputs flash on and off every two seconds.
• Your task is to create a flowchart so that:
  • when the Sun is down(off), all the three outputs will flash
  • when the Sun is up (on), all the outputs should be off.
• Test your flowchart by clicking on the Sun to turn it on and off.
• Screenshot your working flowchart and upload to Bourne to Learn.

• Now you are familiar with how the software Flowol works.
• The above mimic has all three outputs flash on and off.
• follow the steps shown in the image below to create a flash function:

• Once you have created a function, the side menu will now have Sub block for you to use the functions you have created.

• Modify your flowchart from the Gold badge task to use this function.
• Test your flowchart as you have done with your Gold badge and upload the screenshot of your working flowchart to Bourne to Learn.

In this lesson, you…

• Learnt how to use flowcharts to illustrate the flow of the problem solving process.
• Used decomposition to break a problem down into more manageable chunks.

Next lesson, you will…

• Continue to use Flowol to create flowcharts to follow a sequence in an algorithm.

• Finish decomposing the problem by finishing all steps required to reach a solution.
• Create a flowchart using appropriate symbols for your steps.
• Upload both your steps and flowchart to www.bournetolearn.com.

• The above flowchart will make the three outputs flash on and off every two seconds.
• Your task is to create a flowchart so that:
  • when the Sun is down(off), all the three outputs will flash
  • when the Sun is up (on), all the outputs should be off.
• Test your flowchart by clicking on the Sun to turn it on and off.
• Screenshot your working flowchart and upload to Bourne to Learn.

• Upload a screenshot of your function code.