OCR J277 · Component 2 · Topic 2.2.1a

Programming Fundamentals
Variables, Constants & Data Types

Variable · Constant · Integer · Real · Boolean · Character · String · Casting · Operators

CSZone OCR GCSE Computer Science J277

Learning Objectives

By the end of this video you will be able to...

Define a variable and a constant — explain the difference and when to use each one

Identify and choose between the 5 data types: Integer, Real, Boolean, Character and String — and justify your choice

Understand casting — why it is needed, especially because input() always returns a String in Python

Recognise and use all arithmetic, comparison and Boolean operators on the OCR J277 spec

Write assignment, input and output statements correctly in both OCR ERL pseudocode and Python — and avoid the classic exam mistakes

⚡ Topics 2.2.1 and 2.2.2 are combined here. The OCR exam tests variables, constants, operators and data types together.

Variables

Variables — named memory locations

DEFINITION

A variable is a named location in memory that stores a value which can change during program execution. The name stays fixed; the value inside can be overwritten at any time.

ASSIGNMENT SYNTAX

OCR ERL: name ← value

Python: name = value

NAMING CONVENTIONS

Use meaningful names — no spaces. Use camelCase (playerScore) or underscore (player_score). Avoid single letters unless writing a loop counter.

PSEUDOCODE & PYTHON EXAMPLES

OCR ERL

score ← 0 playerName ← "Alice" score ← score + 10 ← value changes — that's fine

PYTHON

score = 0 player_name = "Alice" score = score + 10 # score is now 10

⚡ The right-hand side is always evaluated first, then stored in the variable on the left. So score ← score + 10 reads the current value of score, adds 10, and puts the result back into score.

Constants

Constants — fixed values that cannot change

DEFINITION

A constant is a named value that is set once and cannot change during program execution. Unlike a variable, reassigning a constant should not be allowed.

WHY USE CONSTANTS?

Code is easier to read — TAX_RATE is clearer than a bare 0.2 scattered through the program

Change the value once in one place — it updates everywhere in the program automatically

Prevents accidental modification of values that must stay fixed

OCR ERL — uses const keyword

const TAX_RATE ← 0.2 const MAX_LIVES ← 3 const PI ← 3.14159 const PASS_MARK ← 50

PYTHON — UPPER_CASE convention only

TAX_RATE = 0.2 MAX_LIVES = 3 PI = 3.14159 PASS_MARK = 50

⚠ EXAM NOTE

Python has no built-in constant keyword — UPPER_CASE is a naming convention only. OCR ERL uses the const keyword. In exam pseudocode, always write const.

Data Types

The five data types — 2.2.2

Integer

Whole numbers — no decimal point
age = 16 score = -5 count = 0

Real / Float

Numbers with a decimal point
price = 4.99 temp = 36.7

Boolean

Only True or False — used in conditions and flags
game_over = False is_valid = True

Character

Single character only — one letter, digit or symbol
grade = 'A' key = '?'

String

Sequence of zero or more characters
name = "Alice" msg = ""

EXAM TIP — CHOOSING THE RIGHT TYPE

Number of students → Integer
Temperature → Real
Logged in? → Boolean
Menu option letter → Character
Full name → String

Casting

Casting — temporarily converting data types

WHAT IS CASTING?

Casting temporarily converts a value from one data type to another. The string "42" is not the same as the integer 42 — you must cast to use it in arithmetic.

⚠ WHY CASTING IS NEEDED

input() always returns a String — even when the user types a number. You must cast to Integer or Real before doing arithmetic, or Python will throw a TypeError at runtime.

CASTING FUNCTIONS — same in ERL and Python

int(x)

→ Integer

float(x)

→ Real

str(x)

→ String

bool(x)

→ Boolean

WITHOUT CASTING — BREAKS AT RUNTIME

age = input("Enter age: ") # String! years_left = 65 - age # ❌ TypeError

WITH CASTING — CORRECT

age = int(input("Enter age: ")) # Integer ✓ years_left = 65 - age # ✅ works

OCR ERL EQUIVALENT

age ← int(input("Enter age: ")) yearsLeft ← 65 - age

Arithmetic Operators

Arithmetic operators — + − * / MOD DIV ^

STANDARD OPERATORS

+Addition5 + 3 → 8

-Subtraction10 - 4 → 6

*Multiplication6 * 7 → 42

/Division (real result)7 / 2 → 3.5

INTEGER & POWER OPERATORS

MODRemainder after division10 MOD 3 → 1

DIVInteger quotient10 DIV 3 → 3

^Exponentiation (power)2 ^ 8 → 256

MOD vs DIV — MEMORY AID

Think of 17 ÷ 5: it goes 3 times with 2 left over.
17 DIV 5 → 3 (how many times it fits)
17 MOD 5 → 2 (the remainder)

⚠ PYTHON USES DIFFERENT SYMBOLS

ERL MOD → Python %
ERL DIV → Python //
ERL ^ → Python **

OCR exams use ERL notation — use MOD, DIV and ^ unless told otherwise.

# OCR ERL result ← 17 MOD 5 ← 2 result ← 17 DIV 5 ← 3 result ← 2 ^ 8 ← 256

Comparison Operators

Comparison operators — == != < <= > >=

EQUALITY & LESS-THAN

==Equal to5 == 5 → True

!=Not equal to5 != 3 → True

<Less than3 < 7 → True

<=Less than or equal to5 <= 5 → True

GREATER-THAN

>Greater than9 > 4 → True

>=Greater than or equal to3 >= 3 → True

WHAT THEY RETURN

Comparison operators always return a Boolean — True or False. Nothing else. This is why they work inside IF conditions and WHILE loops.

OCR ERL EXAMPLE

IF score >= 50 THEN print("Pass") ELSE print("Fail") ENDIF

⚡ == checks equality; ← (ERL) or = (Python) is assignment. Never use a single = inside an IF condition.

Boolean Operators

Boolean operators — AND, OR, NOT

AND

BOTH conditions must be True

True AND True → True
True AND False → False

IF age >= 16 AND hasID == True THEN

OR

At least ONE condition must be True

True OR False → True
False OR False → False

IF choice == "Y" OR choice == "y" THEN

NOT

REVERSES the Boolean value

NOT True → False
NOT False → True

IF NOT gameOver THEN

COMBINED EXAMPLE — OCR ERL

IF (score >= 40 AND attended == True) OR bonus == True THEN print("Eligible for certificate") ENDIF WHILE NOT gameOver DO playRound() ENDWHILE

⚡ Use brackets to make the intended order of evaluation clear — (A AND B) OR C is different from A AND (B OR C). When in doubt, bracket it.

Input · Output · Assignment

Input, output and assignment

INPUT

OCR ERL

name ← input("Enter name: ") age ← int(input("Enter age: "))

PYTHON

name = input("Enter name: ") age = int(input("Enter age: "))

OUTPUT

OCR ERL

print(name) print("Hello, " + name)

PYTHON

print(name) print("Hello,", name)

ASSIGNMENT

The right-hand side is evaluated first, then stored in the variable on the left.
ERL: variable ← expression
Python: variable = expression

FULL WORKED EXAMPLE — OCR ERL

name ← input("Enter your name: ") age ← int(input("Enter your age: ")) yearsLeft ← 65 - age print(name + " retires in " + str(yearsLeft) + " years")

⚡ To concatenate an integer into a string for output, cast it back to String with str() first — otherwise you get a TypeError.

Exam Practice

Variables, constants & data types — exam questions

Question 1 — 1 mark

Which data type stores only the values True or False?

Answer — Q1

Boolean — stores only True or False. (1 mark)

Question 2 — 2 marks

A Python program uses age = input("Enter age: "). Explain why casting is needed before calculating how many years until retirement age of 65.

Answer — Q2

input() always returns a String [1] — a String cannot be used in arithmetic (subtracted from 65), so it must be cast to an Integer using int() first [1]

Question 3 — 3 marks

Write OCR ERL pseudocode to ask the user for a number, store it as an integer called num, then output the square of num. Use the correct assignment operator and exponentiation operator for OCR ERL.

Exam Answers

Question 3 — answer and mark scheme

Q3 MARK SCHEME

num ← int(input("Enter a number: ")) ← [1] input used ← [1] int() cast applied print(num ^ 2) ← [1] ^ for exponentiation

Also accept: print(num * num) for the third mark.

COMMON MARK LOSSES ON THIS Q

• Using num = ... instead of num ← ... (wrong assignment operator for ERL)
• Using ** instead of ^ (Python operator, not ERL)
• Forgetting the int() cast around input()

OCR ERL vs PYTHON OPERATORS

Operation	OCR ERL	Python
Exponentiation	^	**
Integer division	DIV	//
Modulus	MOD	%
Assignment	←	=

CASTING QUICK REFERENCE

Target type	ERL function	Python
Integer	int(x)	int(x)
Real	float(x)	float(x)
String	str(x)	str(x)

⚡ The exam will often give you Python code and ask about OCR ERL, or vice versa. Always check which language is specified — operators and assignment syntax differ. ← is ERL only; = is Python only.

Common Mistakes

Common mistakes — avoid these in the exam

MISTAKE 1 — Wrong assignment operator in OCR ERL

Writing x = 5 in OCR ERL pseudocode — this is Python syntax, not ERL

✓ OCR ERL requires the arrow: x ← 5

MISTAKE 2 — Forgetting to cast input()

Writing age = input("Age: ") then doing arithmetic — causes a TypeError at runtime

✓ Always cast on the same line: age = int(input("Age: "))

MISTAKE 3 — Confusing MOD and DIV

Saying 10 MOD 3 = 3 — MOD gives the remainder, not the quotient

✓ 10 MOD 3 = 1 (remainder) | 10 DIV 3 = 3 (quotient)

MISTAKE 4 — Mixing up ERL and Python operator symbols

Using 2 ** 8 in OCR ERL pseudocode, or 10 % 3 instead of 10 MOD 3

✓ ERL: ^ MOD DIV | Python: ** % //

Summary

Key points — 2.2.1a

Variables store changeable values (x ← 5); constants store fixed values (const MAX ← 10) and use the const keyword in OCR ERL

Five data types: Integer Real Boolean Character String — always choose the most appropriate type for the data being stored

Casting converts between types — int(), float(), str(); input() always returns a String — always cast before arithmetic

Arithmetic: + − * / MOD DIV ^ · Comparison: == != < <= > >= · Boolean: AND OR NOT

OCR ERL: assign with ←, power with ^, remainder with MOD · Python: assign with =, power with **, remainder with %

⚡ Next topic: 2.2.1b — Sequence, Selection & Iteration — IF statements, FOR loops and WHILE loops in detail.

2.2.1a Complete

Variables, Constants
& Data Types

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Next Up

2.2.1b — Sequence, Selection & Iteration

Programming FundamentalsVariables, Constants & Data Types

By the end of this video you will be able to...

Variables — named memory locations

Constants — fixed values that cannot change

The five data types — 2.2.2

Casting — temporarily converting data types

Arithmetic operators — + − * / MOD DIV ^

Comparison operators — == != < <= > >=

Boolean operators — AND, OR, NOT

Input, output and assignment

Variables, constants & data types — exam questions

Question 3 — answer and mark scheme

Common mistakes — avoid these in the exam

Key points — 2.2.1a

Variables, Constants& Data Types

Programming Fundamentals
Variables, Constants & Data Types

Variables, Constants
& Data Types