Explaining Algorithms (Cambridge (CIE) O Level Computer Science)
Revision Note
Written by: Robert Hampton
Reviewed by: James Woodhouse
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?
Pseudocode |
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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.
Count ← 0
REPEAT
INPUT Score[Count]
IF Score[Count] >= 70 THEN
Grade[Count] ← "A"
ELSE
IF Score[Count] >= 60 THEN
Grade[Count] ← "B"
ELSE
IF Score[Count] >= 50 THEN
Grade[Count] ← "C"
ELSE
IF Score[Count] >= 40 THEN
Grade[Count] ← "D"
ELSE
IF Score[Count] >= 30 THEN
Grade[Count] ← "E"
ELSE
Grade[Count] ← "F"
ENDIF
ENDIF
ENDIF
ENDIF
ENDIF
Count ← Count + 1
UNTIL Count = 30Describe 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]
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