AQA 7517 · Paper 1 · 4.1.1d

Sequence, Assignment
& Input / Output

AQA A-Level Computer Science · Section 4.1 Fundamentals of Programming

WHAT YOU'LL LEARN

Sequence construct · Assignment operator ← · USERINPUT & OUTPUT

AQA SPEC LINK

4.1.1 — Three constructs: sequence, selection, iteration

Sequence

Sequence — The First Construct

In sequence, instructions execute one after another, in the order written. Every line runs — no skipping.

AQA EXAMPLE

name ← USERINPUT
age ← INT(USERINPUT)
OUTPUT "Hello " + name
OUTPUT "You are " + STR(age) + " years old"

Selection and iteration are exceptions to pure sequence — they alter the flow of execution.

Assignment

The Assignment Operator ←

HOW IT WORKS

Right side evaluated first, result stored in left side variable.

x ← 5
x ← x + 1 → x becomes 6

⚠️ IMPORTANT

x ← x + 1 is NOT a maths equation. It means "take x, add 1, store result back in x". AQA uses ← ; Python uses =

INPUT

Getting Input — USERINPUT

AQA PSEUDOCODE

name ← USERINPUT
age ← INT(USERINPUT)
score ← REAL(USERINPUT)

PYTHON

name = input()
age = int(input())
score = float(input())

USERINPUT always returns a STRING. Cast to INT or REAL before arithmetic!

OUTPUT

Displaying Output

AQA PSEUDOCODE

OUTPUT "Hello, World!"
OUTPUT "Score: " + STR(score)
OUTPUT name + " scored " + STR(score) + "%"

CONCATENATION RULE

Use + to join strings. Numbers must be wrapped in STR() first.

PYTHON PRINT

print("Hello!")
print(f"Score: {score}")
print(name, "scored", score)

Full Program

Sequence: Complete Example

TEMPERATURE CONVERTER (°C → °F)

OUTPUT "Enter temperature in Celsius:"
celsius ← REAL(USERINPUT)
fahrenheit ← (celsius * 9/5) + 32
OUTPUT STR(celsius) + "°C = " + STR(fahrenheit) + "°F"

Pure sequence — 4 lines, each executed in order. Note: cast USERINPUT to REAL; use STR() before concatenation.

Trace Table

Tracing Sequential Code

a ← 10 b ← 3 c ← a * b + 2 a ← a + b OUTPUT a, b, c

Line	a	b	c	Output
a ← 10	10	—	—
b ← 3	10	3	—
c ← a*b+2	10	3	32
a ← a+b	13	3	32
OUTPUT	13	3	32	13, 3, 32

Common Errors

Avoid These Mistakes

❌ Using variable before assigning

OUTPUT score

score has no value yet — assign first

❌ Forgetting type casting on input

total ← USERINPUT + 10

Fix: total ← INT(USERINPUT) + 10

❌ Concatenating number without STR()

OUTPUT "Answer: " + result

Fix: OUTPUT "Answer: " + STR(result)

AQA Exam Style

Practice Question

AQA 7517 — Paper 1 Style

A student writes:
num1 ← INT(USERINPUT)
num2 ← INT(USERINPUT)
total ← num1 + num2
average ← total / 2
OUTPUT "Average: " + STR(average)
The user enters 7 then 13. What is the output?

[2 marks]

1 mark

total = 20; average = 20 / 2 = 10.0

1 mark

Output: Average: 10.0

Summary

Key Points to Remember

Sequence — instructions execute in written order, top to bottom

Assignment ← — evaluate right, store in left. AQA uses ← ; Python uses =

USERINPUT — always returns STRING; cast with INT() or REAL()

OUTPUT — concatenate with + ; numbers need STR() conversion first

Trace tables: track each variable after every assignment

🎉 Lesson complete — move to the quiz!