Explaining Algorithms (Cambridge International IGCSE Computer Science)

Spec point — 3 Explain the purpose of a given algorithm

Explaining Algorithms

How do you explain an algorithm?

• A well designed algorithm should be able to be interpreted by a new user and they should be able to explain what it does

• Algorithms can be written using flowcharts, pseudocode or high-level programming language code such as Python

• The purpose of an algorithm is to solve a problem, if a user does not know the goal of the algorithm, then following the algorithm instructions should make its purpose clear

• If the algorithm is complex then additional ways to understand the problem could be:

  • Look for comments in the code
  • Consider the context of where the algorithm is being used
  • Test the algorithm with different inputs

• Look at the following algorithm, can you explain what it does?

• The purpose of the algorithm is to add ten user-entered numbers together and output the total

• The processes are:

  • initializing three variables (Count, Number, Total)
  • inputting a user number
  • adding to two variables (Total, Count)
  • repeating nine more times
  • outputting the final Total value

Worked Example The pseudocode algorithm shown has been written by a teacher to enter marks for the students in her class and then to apply some simple processing.

Describe what happens in this algorithm.

[3]

Answer

Any 3 of:

• Inputted marks are stored in the array Score[] [1]
• Marks are then checked against a range of boundaries [1]
• A matching grade is assigned to each mark that has been input [1]
• The grade is then stored in the array Grade[] [1]
• At the same index as the inputted mark [1]
• The algorithm finishes after 30 marks have been input [1]