Explaining Algorithms
- Algorithms can be written using flowcharts, pseudocode or high-level programming language code such as Python
- The purpose of an algorithm is to achieve some goal. It isn’t always initially clear what the goal may be. By following the algorithm instructions, the purpose can become clear
Exam Tip
- Comments in an algorithm or program usually describe why something has been done or provide useful information to the reader. Each line of code should otherwise be self-explanatory
- The purpose of the algorithm below 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
Count ← 1
Number ← 0
Total ← 0
REPEAT
INPUT Number
Total ← Total + Number
Count ← Count + 1
UNTIL Count > 10
OUTPUT Total
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 = 30
Describe what happens in this algorithm.
[3]
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]
