课 17, 主题 3

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How To Answer Trace Table Questions Ocr

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Exam code:J277

How do I answer an OCR GCSE (9-1) Computer Science trace table question?

What is a trace table?

Trace tables are used to follow the values of variables as a program runs
These questions test your ability to simulate code line by line and accurately record outputs

Examiner Tips and Tricks

You must read the code carefully and simulate it exactly as a computer would
Use a pencil and annotate each step
The most common mistake is skipping or misreading a line

What you need to know

You may be asked to complete a trace table, explain a trace table, or spot errors in output
These questions are normally worth 3–6 marks
Most commonly appear in questions involving iteration, selection, and arrays/lists
In most cases, the structure of the table is provided, your task is to complete the missing values

Command words to look out for

Command word	What it means
Complete	Fill in the table with correct values
State	Give the value/output/result (usually a single word or number)
Explain	Say why something happens or changes in the program
Identify	Spot where something goes wrong or doesn’t match expectations

How to tackle a trace table question

Follow these steps to answer trace table questions accurately:

Read the code carefully

Understand what each line does

Look out for loops, IF statements, and variable changes
Use the trace table provided
Use the headings and row count to guide how many iterations or steps are needed
Work line by line
Simulate the program in your head or on paper

Update each variable after every change
Watch out for variable resets
Variables declared inside loops often reset every time, don’t carry the wrong value across iterations
Show the final output clearly
If you’re asked for the output, make sure it’s written exactly as it would appear on screen

Worked example

Question

This algorithm calculates the number of points a student gets for the distance they throw in the javelin:

01 javelinThrow = input("Enter distance")
02 yearGroup = input("Enter year group")
03 if javelinThrow >= 20.0 then
04 score = 3
05 elseif javelinThrow >= 10.0 then
06 score = 2
07 else
08 score = 1
09 endif
10 if yearGroup != 11 then
11 score = score * 2
12 endif
13 print("The score is", score)

Complete the trace table for the algorithm when a student in year 10 throws a distance of 14.3

You may not need to use all the rows in the table

`Line number`	`javelinThrow`	`yearGroup`	`score`	`Output`

Read the code carefully

Line 1: It asks you to type in the javelin distance and stores it in a variable called javelinThrow
Line 2: It asks for your year group (like “10” or “11”) and stores it in yearGroup
Lines 3–9: It decides how many points to give you:
- If your throw was 20 metres or more, you get 3 points
- If your throw was 10 metres or more, you get 2 points
- If your throw was less than 10 metres, you get 1 point
Lines 10–12: It checks if you are not in Year 11:
- If you’re not in Year 11, your score is doubled
- If you are in Year 11, your score stays the same
Line 13: It prints your final score

Use the trace table provided

The trace table contains six blank lines which give you an indication of how many times a change/output is required
If you get to the end and you have only completed 2/3 lines, check again, something is probably wrong

Work line by line

01 javelinThrow = input("Enter distance")

14.3

02 yearGroup = input("Enter year group")

03 if javelinThrow >= 20.0 then

04 score = 3

05 elseif javelinThrow >= 10.0 then

Yes

06 score = 2

score = 2

Watch out for variable resets

This program contains no loops

Show the final output clearly

13 print("The score is", score)

The score is 4

Final answer

Computer Science GCES OCR