4th Form
Name:
PREP
Computer Science
Date: 10/10/2023
Marks: / 25
L.O: Decomposition & Abstraction. Trace tables
Computational thinking: thinking like a computer scientist. It’s all about the
steps you take to find the best solution to a complex problem.
Computer scientists rely on decomposition, abstraction and algorithmic thinking
to help them turn a complex problem into small problems that a computer can
help them to solve.


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Decomposition: breaking a complex problem down into smaller problems
and solving each one individually.
Abstraction: picking out the important bits of information from the problem,
ignoring the specific details that don’t matter.
Algorithmic thinking: a logical way of getting from the problem to the
solution. If the steps you take to solve a problem follow an algorithm, then
they can be reused and adapted to solve similar problems in the future.
Questions
You have been asked to produce an algorithm that calculates the approximate
cost of a car journey for four adults of average weight in a 1.4 litre blue Ford Fiesta
(2012).
1. Decompose the problem into a series of sub-problems and list those subproblems below.
[5]
Abstract information that is not relevant and list the information below.
[3]
2. Produce an algorithm using a flowchart or pseudocode that calculates the cost
of the journey.
[5]
Trace tables:
Trace tables are tables that consist of columns. Each column can represent a
variable, a condition, or an output. Not every variable, condition or output in an
algorithm needs a column in a trace table.
The purpose of the table is that we can run through an algorithm and simulate
what a computer would do if the program were to execute. We complete the table
to show how the variables change, what the conditions would resolve to, and/or
what outputs would be displayed.
There are two main reasons that trace tables are used. The first is to determine
what an algorithm does by running through it to see what happens as the
algorithm runs. The second is to test the logic of an algorithm if there are errors
that are not easily spotted.
Questions
Complete the trace tables:
FOR x  1 TO 3
x
y
Output
FOR y  1 TO 2
OUTPUT ( x * y )
ENDFOR
ENDFOR
[6]
x1
WHILE x < 5
OUTPUT (x*2)
x
xx+1
ENDWHILE
OUTPUT "The end"
[6]
x<5
Output