3.1.1b Representing Algorithms — AQA 8525

Representing Algorithms

Algorithms can be represented in several ways before they are coded. The AQA 8525 specification requires you to understand and use flowcharts and pseudo-code. Both are ways of expressing the logic of an algorithm without tying it to a specific programming language.

Flowcharts

A flowchart is a diagram that uses standard shapes connected by arrows to show the steps and decisions in an algorithm. Arrows show the flow of control — the order in which steps are executed.

Standard Flowchart Symbols

Shape	Name	Used for
Oval	Terminator	Start and End of the algorithm
Rectangle	Process	A calculation or action, e.g. x ← x + 1
Parallelogram	Input / Output	Reading input from a user or displaying output
Diamond	Decision	A yes/no question — creates two branches
Rectangle+	Subroutine	A call to a named subroutine (sub-program)

Rules for flowcharts

Every flowchart must have a Start and an End terminator
Decision boxes must have exactly two exits labelled Yes and No (or True/False)
Arrows must show direction of flow — never ambiguous
All paths through the flowchart must eventually reach the End terminator

Example: Check if a number is positive

START → Input number → Is number > 0? → Yes: Output "Positive" → END; No: Output "Not positive" → END

Pseudo-code

Pseudo-code is a structured way of writing algorithm steps using English-like statements and programming constructs (variables, loops, conditions) without the exact syntax of any real language. AQA provides its own pseudo-code notation that you must learn.

AQA Pseudo-code Notation

Variables and assignment

x ← 5          # assign the value 5 to variable x
name ← 'Alice'  # assign a string
total ← a + b  # assign a calculated value

Input and Output

x ← INPUT('Enter a number: ')
OUTPUT('The answer is ', result)

Selection (IF statements)

IF x > 0 THEN
    OUTPUT('Positive')
ELSE
    OUTPUT('Not positive')
ENDIF

Count-controlled loops (FOR)

FOR i ← 1 TO 10
    OUTPUT(i)
ENDFOR

Condition-controlled loops (WHILE and REPEAT)

WHILE x > 0
    x ← x - 1
ENDWHILE

REPEAT
    x ← x - 1
UNTIL x = 0

Subroutines

SUBROUTINE greet(name)
    OUTPUT('Hello ', name)
ENDSUBROUTINE

greet('Alice')   # call the subroutine

Trace Tables

A trace table is a way of manually working through an algorithm step by step, recording how the values of variables change at each stage. They are used to:

Verify that an algorithm produces the correct output
Find bugs (errors in logic)
Understand what an algorithm does

Example trace table for a simple loop

total ← 0
FOR i ← 1 TO 3
    total ← total + i
ENDFOR
OUTPUT(total)

Step	i	total	OUTPUT
Start	–	0	–
i = 1	1	1	–
i = 2	2	3	–
i = 3	3	6	–
End	–	–	6

Flowcharts vs Pseudo-code

Flowcharts	Pseudo-code
Visual — good for seeing flow of control	Textual — closer to real code
Easy to follow for non-programmers	Better for complex algorithms
Standard shapes everyone recognises	More compact for long algorithms
Harder to write loops with many iterations	Loops and conditions are easy to write

Exam tip: AQA exam questions often ask you to write pseudo-code in AQA notation, or to trace through given pseudo-code with a trace table. Practise both skills. The ← symbol (not =) is used for assignment in AQA pseudo-code.

⚠️ Common Mistakes

Using = for assignment in AQA pseudo-code — use ← instead
Forgetting ENDIF, ENDFOR, ENDWHILE, ENDSUBROUTINE keywords to close structures
Decision boxes in flowcharts with only one exit — they must have two (Yes/No)
Missing a Start or End terminator in a flowchart
Confusing WHILE (checks first) with REPEAT...UNTIL (checks last, always runs at least once)

▶

Video coming soon

This lesson video is in production

Key points covered in this video

All five standard flowchart symbols and when to use each
AQA pseudo-code notation: variables, INPUT/OUTPUT, IF, FOR, WHILE, REPEAT
How to construct a trace table and use it to find bugs
Comparison of flowcharts and pseudo-code — which to use when
Worked exam question: write pseudo-code and draw a flowchart for the same algorithm

Click slide or press arrow keys to navigate

✍️

Exam-style Worksheet — 3.1.1b Representing Algorithms

8 AQA-style questions · 19 marks total · AI will mark your answers and give feedback

Q1State the flowchart symbol used for a decision.[1 mark]

✅ Mark scheme

Mark scheme

Diamond (rhombus) shape. [1 mark]

Q2State the flowchart symbol used for input and output operations.[1 mark]

✅ Mark scheme

Mark scheme

Parallelogram. [1 mark]

Q3Explain the difference between a WHILE loop and a REPEAT...UNTIL loop.[2 marks]

✅ Mark scheme

Mark scheme

WHILE checks its condition before executing the body, so it may never execute if the condition is false from the start [1]; REPEAT...UNTIL checks its condition after executing the body, so it always executes at least once [1].

Q4Write AQA pseudo-code to ask a user to enter their age and output "Adult" if age ≥ 18 or "Minor" otherwise.[4 marks]

✅ Mark scheme

Mark scheme

age ← INPUT('Enter your age: ') [1]; IF age >= 18 THEN [1]; OUTPUT('Adult') [1]; ELSE OUTPUT('Minor') ENDIF [1]. Must use ← for assignment; must have ENDIF; must have both branches.

Q5Write AQA pseudo-code to output the numbers 1 to 5 using a FOR loop.[3 marks]

✅ Mark scheme

Mark scheme

FOR i ← 1 TO 5 [1]; OUTPUT(i) or equivalent [1]; ENDFOR [1].

Q6Trace through the following pseudo-code and complete a trace table showing the value of count and total at each step.

count ← 0
total ← 0
WHILE count < 4
count ← count + 1
total ← total + count
ENDWHILE[4 marks]

✅ Mark scheme

Mark scheme

count=0, total=0 (start) [1]; count=1, total=1 [1]; count=2, total=3 [1]; count=3, total=6; count=4, total=10 (loop ends as count is no longer < 4) [1]. Final value of total = 10.

Q7Give TWO advantages of using pseudo-code over a flowchart when representing a complex algorithm.[2 marks]

✅ Mark scheme

Mark scheme (any 2)

More compact — complex algorithms with many steps would require a very large flowchart [1]; easier to write loops [1]; closer to actual programming code so easier to convert [1]; easier to edit and rewrite [1].

Q8A flowchart has a decision box that checks "Is score ≥ 50?". Describe what must happen after a decision box, and what the two exits must be labelled.[2 marks]

✅ Mark scheme

Mark scheme

A decision box must have exactly two exits [1]; they must be labelled Yes and No (or True and False) [1].

—

Compare your answers to the mark schemes above

Topic Quiz

Question 1 of 15

You scored

out of 15

Card 1 of 8

Click to flip

🎉

All cards reviewed!

Term	Definition

🔒

Pro Content

Subscribe to unlock all AQA 8525 lessons, worksheets, quizzes and mini tests.

£7.99/month

or £59/year

Upgrade to Pro

Representing Algorithms

Flowcharts

Standard Flowchart Symbols

Rules for flowcharts

Example: Check if a number is positive

Pseudo-code

AQA Pseudo-code Notation

Variables and assignment

Input and Output

Selection (IF statements)

Count-controlled loops (FOR)

Condition-controlled loops (WHILE and REPEAT)

Subroutines

Trace Tables

Example trace table for a simple loop

Flowcharts vs Pseudo-code

Key points covered in this video

Exam-style Worksheet — 3.1.1b Representing Algorithms

Mini Test — 3.1.1b Representing Algorithms