2.1 Interpreting and Completing Algorithm

Question 1

Interpreting Algorithms

Answer 1

• Given an algorithm you should be able to read it and explain what it does.
• This needs some practice, but there are some things you can look out for.

Question 2

What to look out for to interpret an algorithm

Answer 2

Look for identifiers
identify Inputs & Outputs
Examine Output messages
Look for comments

Question 3

Look for Identifiers :

Answer 3

• Identifiers are the names of variables, constants, and subroutines.
• These often give strong clues about the purpose of an algorithm.

Question 4

Identify Inputs & Outputs

Answer 4

Check what is being input and output in the algorithm for clues about its purpose.

Question 5

Examine Output Messages

Answer 5

Output messages often format the result of an algorithm in a human readable way.

Question 6

Look for comments

Answer 6

Look for comments

Question 7

Correcting Algorithms

Answer 7

Incorrect Operators
Look out for the difference between similar operators such as testing if a number is less than another, rather than less than or equal to the other

Incorrect Identifiers -
A common mistake in programs is incorrect identifiers.
- Be very careful with uppercase and lowercase letters.
- Be careful with similar looking characters:
- 0 and O.
- 1 and l (lower case L)

Missing processes
Sometimes a line of code has been forgotten, which can lead to issues such as infinite loops, where the code will never end.

Question 8

Completing Algorithms

Answer 8

Interpreting the diagrams

• The first step for this type of question is to try to identify what the algorithm does.
• If you can interpret the algorithm, then it will be much easier to follow it.

Trace tables

• You can draw a table with a column for each variable in the algorithm.
• Use this table to record the value of each variable, and carefully follow through the code until the end.
• Finally, the trace table should include your answer.