Data Structures & Sub-Programs (Edexcel GCSE Computer Science)

Revision Note

Written by: Robert Hampton

Reviewed by: James Woodhouse

Data Structures

What is a data structure?

A data structure provides a structured way to store data, which makes it easy to access and manipulate
Examples of data structures are:
- Arrays
- Records

Arrays

An array is a sequence of data, of the same data type stored under the same identifier
Elements stored in an array can be identified by an index (position in the array)
Indexes start with the value 0
An array can be both 1-dimensional and 2-dimensional

Records

A record is a sequence of data, usually of mixed data types with a fixed length
Elements stored in an array can be identified by an index (position in the array)
Indexes start with the value 0

Structure	Example
Arrays	`scores = [1, 4, 2, 6, 2]`
Records	`Students = [001,"Bob", 2.99, "Birmingham"]`

scores[0] holds the value 1
scores[2] holds the value 2
students[3] holds the value "Birmingham"

Examiner Tips and Tricks

Python has it's own data structure called a 'list' which can look like both an array and record BUT they are not the same thing!

In the exam, if a list holds data of all the same type then it can be thought of as an array, if data is different types it can be thought of as a record

Python example
# Create an array of numbers `numbers = [5, 11, 15, 20, 25]` # Access elements by index `first_number = numbers[0]` # Accesses the first element (index 0) `last_number = numbers[-1]` # Accesses the last element (using negative index) # Print the entire array `print("Array:", numbers)` # Modify an element `numbers[2] = 12` # Change the third element (index 2) to 12 # Print the modified array `print("Modified array:", numbers)` # Loop through the array `for number in numbers:` `print("Number:", number)`

Python example

# Create an array of numbers

numbers = [5, 11, 15, 20, 25]

# Access elements by index

first_number = numbers[0] # Accesses the first element (index 0)

last_number = numbers[-1] # Accesses the last element (using negative index)

# Print the entire array

print("Array:", numbers)

# Modify an element

numbers[2] = 12 # Change the third element (index 2) to 12

# Print the modified array

print("Modified array:", numbers)

# Loop through the array

for number in numbers:

print("Number:", number)

1-dimensional & 2-dimensional arrays

Python example
# 1-dimensional array (list of numbers) `numbers = [3, 7, 11, 15]` # Access elements by index `first_number = numbers[0]` `print("First element (1D array):", first_number)` # Loop through the array `for number in numbers:` `print("Number (1D array):", number)` # 2-dimensional array `temperature_data = [` `[20, 25, 30],` # Week 1 temperatures `[22, 27, 29],` # Week 2 temperatures `]` # Access elements by row and column index `week1_monday_temp = temperature_data[0][0]` # Week 1, Monday temperature `print("Week 1, Monday temperature (2D array):", week1_monday_temp)` # Print the entire 2D array `for row in temperature_data:` `print(row)` # Prints each row as a list # Loop through the 2D array (accessing elements) `for week in temperature_data:` `for day in week:` `print("Temperature:", day)`

Python example

# 1-dimensional array (list of numbers)

numbers = [3, 7, 11, 15]

# Access elements by index

first_number = numbers[0]

print("First element (1D array):", first_number)

# Loop through the array

for number in numbers:

print("Number (1D array):", number)

# 2-dimensional array

temperature_data = [

[20, 25, 30], # Week 1 temperatures

[22, 27, 29], # Week 2 temperatures

]

# Access elements by row and column index

week1_monday_temp = temperature_data[0][0] # Week 1, Monday temperature

print("Week 1, Monday temperature (2D array):", week1_monday_temp)

# Print the entire 2D array

for row in temperature_data:

print(row) # Prints each row as a list

# Loop through the 2D array (accessing elements)

for week in temperature_data:

for day in week:

print("Temperature:", day)

Last updated: 9 April 2024

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