Unit 2 Review & Exam Prep — AQA GCSE CS (8525)

Spec & Goals 3 min

AQA Spec 3.2 · Programming (whole unit)

By the end of this lesson you can:

Revise and self-check the whole of Unit 2, spotting your weak topics.
Answer exam questions that span all of spec 3.2, for the marks on offer.
Make a focused revision plan that targets the topics you got wrong.

Warm-Up — command words & the paper 5 min

This is the last lesson of Unit 2. First, know the exam you are sitting.

Command words tell you what to do

Read the command word first — it sets how much to write.

Command word	What it demands
State	A word or short phrase. No explanation.
Describe	Say what something is, or the steps, with detail.
Explain	Give reasons — the how or the why.
Complete	Fill a table, loop or line of code exactly.
Calculate	Work out a value; show your working.

Key Concept — your Unit 2 spec checklist 14 min

Tick each spec point. If you cannot do one, that is a topic to revise tonight.

Spec point	You should be able to…
Data types	Name and use integer, real, Boolean, character and string.
Variables & constants	Declare, assign and use a variable; explain why a constant never changes while the program runs.
Selection	Use `IF … THEN … ELSE … ENDIF` and nested or chained `ELSE IF` to choose a path.
Iteration	Use count-controlled (`FOR`) and condition-controlled (`WHILE`, `REPEAT`) loops.
Arithmetic operators	Use `+ - * /`, integer division `DIV` and remainder `MOD`.
Relational operators	Use `= ≠ < > ≤ ≥` to compare two values and return a Boolean.
Boolean operators	Combine conditions with `AND`, `OR` and `NOT`.
Arrays (1-D & 2-D)	Create, read and write a one-dimensional array and a two-dimensional array using indexes.
Records	Store related fields of different types together as one structured record.
Input / output	Read a value with `USERINPUT` and display one with `OUTPUT`.
Random numbers	Generate a random integer in a range with `RANDOM_INT(a, b)`.
String handling	Find `LEN`, take a substring, change case and join strings with `+`.
Subroutines	Write a procedure and a function; pass parameters and use `RETURN`.
Scope	Tell apart a local variable (one subroutine) from a global one (whole program).
Structured programming	Break a problem into named subroutines with clear inputs and outputs.
Validation	Check input is sensible with range, length, presence and format checks.
Authentication	Confirm a user's identity, e.g. with a username and password.
Testing & test data	Choose normal, boundary and erroneous test data to test a program.

Must remember: arrays index from 0. The first element of scores is scores[0], not scores[1].

Function vs procedure: a function returns a value with RETURN; a procedure does a job but returns nothing.

DIV and MOD: 17 DIV 5 is 3 (whole divisions); 17 MOD 5 is 2 (the remainder). Examiners love this pair.

Worked Example — a full multi-part question 12 min

Here is one question with three parts. We earn the marks aloud.

AQA pseudo-code

01  total ← 0
02  FOR i ← 0 TO 2
03      total ← total + scores[i]
04  ENDFOR
05  average ← total DIV 3
06  OUTPUT average

The array scores holds [8, 5, 5].

Part (a) — Complete the trace table. [3 marks]

We follow the loop line by line, writing i and total after each pass.

i	total	average	OUTPUT
—	0
0	8
1	13
2	18
		6
			6

Each correct value of total after a pass earns a mark.

Part (b) — State the output. [1 mark]

The total is 18; 18 DIV 3 is 6. The output is 6 (1).

Part (c) — A score must be from 0 to 10. Name a suitable validation check. [1 mark]

A range check (1) — it accepts a score only if it is between 0 and 10 inclusive.

How the marks are earned: trace each pass in order (a), apply DIV to read the final output (b), then name a check that fits the rule given (c). The command word name wants the term, not a description.

Try It Yourself — timed mini-paper 12 min

Give yourself 12 minutes. Write full answers; check them with your teacher.

🟢 Q1

State the data type best suited to store a person's age, and one to store whether they are a member. [2 marks]

🟡 Q2

Calculate the value of 23 DIV 4 and the value of 23 MOD 4. [2 marks]

🟡 Q3

Complete the missing line so this loop outputs the numbers 1 to 5.

01  FOR i ← 1 TO 5
02      __________
03  ENDFOR

[1 mark]

🔴 Q4

Describe the difference between a local variable and a global variable. [2 marks]

🔴 Q5

Explain why a function is used instead of a procedure when a calculated result is needed. [2 marks]

📝 Exam Practice 10 min

These questions span the whole of Unit 2. Match your answer to the command word and the marks.

Calculate[2 marks]

Calculate the value of 29 DIV 6 and the value of 29 MOD 6.

Mark scheme

29 DIV 6 = 4 (1).
29 MOD 6 = 5 (1).

Complete[1 mark]

Complete the missing condition so the loop stops once count reaches 10.

01  count ← 0
02  WHILE ____________
03      count ← count + 1
04  ENDWHILE

Mark scheme

count < 10 (1). Accept count ≠ 10 / count <= 9.

Describe[2 marks]

Describe the difference between a procedure and a function.

Mark scheme

A function returns a value to the line that called it (1).
A procedure carries out a task but does not return a value (1).

Give[3 marks]

A field accepts a percentage from 0 to 100. Give one normal, one boundary and one erroneous test value.

Mark scheme

Normal: any value clearly inside the range, e.g. 57 (1).
Boundary: a value on the edge, e.g. 0 or 100 (1).
Erroneous: a value that should be rejected, e.g. -1 or 150 (1).

State[1 mark]

An array names holds ["Ali", "Bo", "Chen"]. State the value of names[2].

Mark scheme

"Chen" (1) — arrays index from 0, so index 2 is the third element.

Recap & Key Terms 3 min

Use your mini-paper marks to plan tonight's revision.

Muddled the data types or operators? Redo CS-L2-01 and CS-L2-02.
Tripped on selection or iteration? Redo CS-L2-03 and CS-L2-04.
Unsure on DIV / MOD or string handling? Redo CS-L2-05.
Lost on arrays or records? Redo CS-L2-06 — remember arrays index from 0.
Mixed up procedures and functions? Redo CS-L2-09 and learn scope.
Slipped on validation or test data? Redo CS-L2-13 and CS-L2-14.

Variable: A named store whose value can change while the program runs.
Constant: A named store whose value is fixed and cannot change while the program runs.
Selection: Choosing between paths with a decision — written as IF … THEN … ELSE … ENDIF.
Iteration: Repeating steps with a count-controlled (FOR) or condition-controlled (WHILE) loop.
DIV: Integer division — the whole number of times one value divides another.
MOD: The remainder left after integer division.
Array: An ordered collection of items of the same type, accessed by an index from 0.
Record: A structure that groups related fields of possibly different types.
Procedure: A named subroutine that carries out a task but does not return a value.
Function: A named subroutine that returns a value with RETURN.
Parameter: A value passed into a subroutine so it can work on different data.
Local variable: A variable that exists only inside the subroutine where it is declared.
Global variable: A variable that can be used anywhere in the program.
Validation: Checking input is sensible, e.g. with a range, length, presence or format check.
Authentication: Confirming a user's identity, for example with a username and password.
Test data: Values chosen to test a program: normal, boundary and erroneous.

Homework 1 min

Task (≤ 15 min): Revisit your weakest topic from the mini-paper. Open that lesson and redo its Exam Practice section.

Bring one question you still find hard to the next session, so we can work through it together.

Spec & Goals 3 min

AQA Spec 3.2 · Programming (whole unit)

By the end of this lesson you can:

Revise and self-check the whole of Unit 2, spotting your weak topics.
Answer exam questions that span all of spec 3.2, for the marks on offer.
Make a focused revision plan that targets the topics you got wrong.

Warm-Up — command words & the paper 5 min

This is the last lesson of Unit 2. First, know the exam you are sitting.

Command words tell you what to do

Read the command word first — it sets how much to write.

Command word	What it demands
State	A word or short phrase. No explanation.
Describe	Say what something is, or the steps, with detail.
Explain	Give reasons — the how or the why.
Complete	Fill a table, loop or line of code exactly.
Calculate	Work out a value; show your working.

Key Concept — your Unit 2 spec checklist 14 min

Tick each spec point. If you cannot do one, that is a topic to revise tonight.

Spec point	You should be able to…
Data types	Name and use integer, real, Boolean, character and string.
Variables & constants	Declare, assign and use a variable; explain why a constant never changes while the program runs.
Selection	Use `IF … THEN … ELSE … ENDIF` and nested or chained `ELSE IF` to choose a path.
Iteration	Use count-controlled (`FOR`) and condition-controlled (`WHILE`, `REPEAT`) loops.
Arithmetic operators	Use `+ - * /`, integer division `DIV` and remainder `MOD`.
Relational operators	Use `= ≠ < > ≤ ≥` to compare two values and return a Boolean.
Boolean operators	Combine conditions with `AND`, `OR` and `NOT`.
Arrays (1-D & 2-D)	Create, read and write a one-dimensional array and a two-dimensional array using indexes.
Records	Store related fields of different types together as one structured record.
Input / output	Read a value with `USERINPUT` and display one with `OUTPUT`.
Random numbers	Generate a random integer in a range with `RANDOM_INT(a, b)`.
String handling	Find `LEN`, take a substring, change case and join strings with `+`.
Subroutines	Write a procedure and a function; pass parameters and use `RETURN`.
Scope	Tell apart a local variable (one subroutine) from a global one (whole program).
Structured programming	Break a problem into named subroutines with clear inputs and outputs.
Validation	Check input is sensible with range, length, presence and format checks.
Authentication	Confirm a user's identity, e.g. with a username and password.
Testing & test data	Choose normal, boundary and erroneous test data to test a program.

Must remember: arrays index from 0. The first element of scores is scores[0], not scores[1].

Function vs procedure: a function returns a value with RETURN; a procedure does a job but returns nothing.

DIV and MOD: 17 DIV 5 is 3 (whole divisions); 17 MOD 5 is 2 (the remainder). Examiners love this pair.

Worked Example — a full multi-part question 12 min

Here is one question with three parts. We earn the marks aloud.

AQA pseudo-code

01  total ← 0
02  FOR i ← 0 TO 2
03      total ← total + scores[i]
04  ENDFOR
05  average ← total DIV 3
06  OUTPUT average

The array scores holds [8, 5, 5].

Part (a) — Complete the trace table. [3 marks]

We follow the loop line by line, writing i and total after each pass.

i	total	average	OUTPUT
—	0
0	8
1	13
2	18
		6
			6

Each correct value of total after a pass earns a mark.

Part (b) — State the output. [1 mark]

The total is 18; 18 DIV 3 is 6. The output is 6 (1).

Part (c) — A score must be from 0 to 10. Name a suitable validation check. [1 mark]

A range check (1) — it accepts a score only if it is between 0 and 10 inclusive.

Try It Yourself — timed mini-paper 12 min

Give yourself 12 minutes. Write full answers; check them with your teacher.

🟢 Q1

State the data type best suited to store a person's age, and one to store whether they are a member. [2 marks]

🟡 Q2

Calculate the value of 23 DIV 4 and the value of 23 MOD 4. [2 marks]

🟡 Q3

Complete the missing line so this loop outputs the numbers 1 to 5.

01  FOR i ← 1 TO 5
02      __________
03  ENDFOR

[1 mark]

🔴 Q4

Describe the difference between a local variable and a global variable. [2 marks]

🔴 Q5

Explain why a function is used instead of a procedure when a calculated result is needed. [2 marks]

📝 Exam Practice 10 min

These questions span the whole of Unit 2. Match your answer to the command word and the marks.

Calculate[2 marks]

Calculate the value of 29 DIV 6 and the value of 29 MOD 6.

Mark scheme

29 DIV 6 = 4 (1).
29 MOD 6 = 5 (1).

Complete[1 mark]

Complete the missing condition so the loop stops once count reaches 10.

01  count ← 0
02  WHILE ____________
03      count ← count + 1
04  ENDWHILE

Mark scheme

count < 10 (1). Accept count ≠ 10 / count <= 9.

Describe[2 marks]

Describe the difference between a procedure and a function.

Mark scheme

A function returns a value to the line that called it (1).
A procedure carries out a task but does not return a value (1).

Give[3 marks]

A field accepts a percentage from 0 to 100. Give one normal, one boundary and one erroneous test value.

Mark scheme

Normal: any value clearly inside the range, e.g. 57 (1).
Boundary: a value on the edge, e.g. 0 or 100 (1).
Erroneous: a value that should be rejected, e.g. -1 or 150 (1).

State[1 mark]

An array names holds ["Ali", "Bo", "Chen"]. State the value of names[2].

Mark scheme

"Chen" (1) — arrays index from 0, so index 2 is the third element.

Recap & Key Terms 3 min

Use your mini-paper marks to plan tonight's revision.

Muddled the data types or operators? Redo CS-L2-01 and CS-L2-02.
Tripped on selection or iteration? Redo CS-L2-03 and CS-L2-04.
Unsure on DIV / MOD or string handling? Redo CS-L2-05.
Lost on arrays or records? Redo CS-L2-06 — remember arrays index from 0.
Mixed up procedures and functions? Redo CS-L2-09 and learn scope.
Slipped on validation or test data? Redo CS-L2-13 and CS-L2-14.

Variable: A named store whose value can change while the program runs.
Constant: A named store whose value is fixed and cannot change while the program runs.
Selection: Choosing between paths with a decision — written as IF … THEN … ELSE … ENDIF.
Iteration: Repeating steps with a count-controlled (FOR) or condition-controlled (WHILE) loop.
DIV: Integer division — the whole number of times one value divides another.
MOD: The remainder left after integer division.
Array: An ordered collection of items of the same type, accessed by an index from 0.
Record: A structure that groups related fields of possibly different types.
Procedure: A named subroutine that carries out a task but does not return a value.
Function: A named subroutine that returns a value with RETURN.
Parameter: A value passed into a subroutine so it can work on different data.
Local variable: A variable that exists only inside the subroutine where it is declared.
Global variable: A variable that can be used anywhere in the program.
Validation: Checking input is sensible, e.g. with a range, length, presence or format check.
Authentication: Confirming a user's identity, for example with a username and password.
Test data: Values chosen to test a program: normal, boundary and erroneous.

Homework 1 min

Task (≤ 15 min): Revisit your weakest topic from the mini-paper. Open that lesson and redo its Exam Practice section.

Bring one question you still find hard to the next session, so we can work through it together.