Input and Output

Programs interact with the user through input (receiving data) and output (displaying data). This lesson covers how to read data from a user, display results, and format output — all essential skills for GCSE Computer Science (AQA 3.2 / OCR J277 2.2).

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Output

Output is how a program communicates results to the user, typically by displaying text on the screen.

Pseudocode

OUTPUT "Hello, World!"
OUTPUT "Your score is: ", score

Python

print("Hello, World!")
print("Your score is:", score)

You can output multiple items by separating them with commas. Python adds a space between items automatically.

Concatenation in Output

You can join (concatenate) strings to build a message:

name = "Alice"
print("Welcome, " + name + "!")
# Output: Welcome, Alice!

When concatenating, all parts must be strings. Use str() to convert numbers:

score = 85
print("Your score is " + str(score))

Alternatively, use f-strings (formatted string literals) in Python 3.6+:

print(f"Your score is {score}")

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Input

Input is how a program receives data from the user, typically via the keyboard.

Pseudocode

name ← USERINPUT
OUTPUT "Enter your age:"
age ← USERINPUT

AQA pseudocode uses USERINPUT to represent keyboard input.

Python

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

Important: In Python, input() always returns a string. If you need a number, you must cast the result.

age = int(input("Enter your age: "))
height = float(input("Enter your height in metres: "))

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I/O Flow

flowchart LR
    U[User] -->|types text| K[Keyboard]
    K --> I[input / USERINPUT]
    I --> V["Variable<br/>always a string"]
    V --> C["Cast int / float<br/>if numeric needed"]
    C --> P[Process / Calculate]
    P --> O[print / OUTPUT]
    O --> S[Screen]
    S --> U

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Combining Input and Output

A typical pattern is to prompt the user, read their input, process it, and display the result:

# Calculate the area of a rectangle
length = float(input("Enter the length: "))
width = float(input("Enter the width: "))
area = length * width
print(f"The area is {area}")

In pseudocode:

OUTPUT "Enter the length:"
length ← REAL(USERINPUT)
OUTPUT "Enter the width:"
width ← REAL(USERINPUT)
area ← length * width
OUTPUT "The area is ", area

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Arithmetic Operators

When processing input, you often perform calculations. The standard arithmetic operators are:

Operator	Meaning	Pseudocode	Python	Example
+	Addition	+	+	5 + 3 = 8
-	Subtraction	-	-	10 - 4 = 6
*	Multiplication	*	*	3 * 7 = 21
/	Division (real)	/	/	7 / 2 = 3.5
DIV	Integer division	DIV	//	7 DIV 2 = 3
MOD	Modulus (remainder)	MOD	%	7 MOD 2 = 1
^	Exponentiation	^	**	2 ^ 3 = 8

DIV and MOD

These are particularly important at GCSE:

• DIV (integer division) gives the whole-number part of a division: 17 DIV 5 = 3
• MOD (modulus) gives the remainder: 17 MOD 5 = 2

Common uses of MOD:

• Checking if a number is even: number MOD 2 == 0
• Extracting digits from a number
• Wrapping values around (e.g. clock arithmetic)

total_minutes = 137
hours = total_minutes // 60   # 2
minutes = total_minutes % 60  # 17
print(f"{hours} hours and {minutes} minutes")

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Comparison Operators

These are used in conditions and return a Boolean value:

Operator	Meaning	Pseudocode	Python
==	Equal to	= or ==	==
!=	Not equal to	≠ or !=	!=
<	Less than	<	<
>	Greater than	>	>
<=	Less than or equal	≤ or <=	<=
>=	Greater than or equal	≥ or >=	>=

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Common Mistakes

1. Forgetting to cast input — comparing "16" with 18 will not work as expected because one is a string.
2. Using = instead of == — in Python, = is assignment while == is comparison.
3. Concatenating a number with a string without converting: "Score: " + 10 causes a TypeError in Python.

Exam Tip: Always show the prompt message inside input() or as a separate OUTPUT statement. Examiners like to see clear, user-friendly prompts.

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Summary

• Output displays information to the user (print() in Python, OUTPUT in pseudocode).
• Input reads data from the user (input() in Python, USERINPUT in pseudocode).
• Input always returns a string — cast to int() or float() as needed.
• Know all arithmetic operators including DIV and MOD.
• Know all comparison operators and that they return Boolean values.

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Extended Worked Examples

Example 1: Unit converter (miles to kilometres)

MILES_TO_KM = 1.60934

miles = float(input("Distance in miles: "))
km = miles * MILES_TO_KM
print(f"{miles} miles is {km:.2f} km")

For input 10:

Variable	Value
miles	10.0
km	16.0934

Expected output: 10.0 miles is 16.09 km

Example 2: Split a total into pounds and pence using DIV and MOD