Arrays (OCR GCSE Computer Science): Revision Note

Create blank 1D array

array scores[5]

scores = [0]*5

Creates an array with 5 elements (0–4), each initialised to 0

Create empty array

n/a

scores = []

Creates an empty list (no elements)

Assignment

colours[4] = "Red"

colours[4] = "Red"

Assigns the colour "Red" to index 4 (5th element)

# Creating a one-dimensional array
array = [1, 2, 3, 4, 5]

# Accessing elements of the array
print(array[0])   # Output: 1
print(array[2])   # Output: 3

# Modifying elements of the array
array[1] = 10
print(array)      # Output: [1, 10, 3, 4, 5]

# Iterating over the array
for element in array:
    print(element)

# Output:
# 1
# 10
# 3
# 4
# 5

# Length of the array
length = len(array)
print(length)     # Output: 5

Create blank 2D array

ARRAY players[3,3]

players = [[None]*3 for _ in range(3)]

Creates a 3x3 2D array with all values set to None

Create populated 2D array

players = [["Rob", "Paul", "Hayley"], [10, 5, 8]]

players = [["Rob", "Paul", "Hayley"], [10, 5, 8]]

Creates a 2D array with names in row 0 and scores in row 1

Assign a value

players[0,1] = "Holly"

players[0][1] = "Holly"

Replaces "Paul" in row 0, column 1 with "Holly"

Access a value

value = players[2,2]

value = players[2][2]

Retrieves the value at row 2, column 2

# Initialising a 2D array with 3 rows and 3 columns, with the specified values
array_2d = [[1, 2, 3],
            [4, 5, 6],
            [7, 8, 9]]

# Accessing elements in the 2D array
print(array_2d[0][0])  # Output: 1
print(array_2d[1][2])  # Output: 6