Arrays (Cambridge (CIE) IGCSE Computer Science): Revision Note

Create

DECLARE scores: ARRAY[1:5]OF INTEGER

scores = []

Creates a blank array with 5 elements (1-5)

Creates a blank array

scores ← [12, 10, 5, 2, 8]

scores = [12, 10, 5, 2, 8]

Creates an array called scores with values assigned

Assignment

colours[4] ← "Red"

colours[4] = "Red"

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

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

DECLARE MyArray : ARRAY[1:5] OF INTEGER

array = [1, 2, 3, 4, 5]

MyArray[1] ← 1

array[index]

MyArray[index] ← newValue

array[index] = newValue

There is no built-in length function in CIE pseudocode. The array length is known from the declaration or stored in a variable.

len(array)

// Creating a one-dimensional array
DECLARE MyArray : ARRAY[1:5] OF INTEGER
MyArray[1] ← 1
MyArray[2] ← 2
MyArray[3] ← 3
MyArray[4] ← 4
MyArray[5] ← 5

// Accessing elements of the array
OUTPUT MyArray[1]          // Output: 1
OUTPUT MyArray[3]          // Output: 3

// Modifying elements of the array
MyArray[2] ← 10
// MyArray is now: [1, 10, 3, 4, 5]

// Iterating over the array
DECLARE Index : INTEGER
FOR Index ← 1 TO 5
    OUTPUT MyArray[Index]
NEXT Index

// Output:
// 1
// 10
// 3
// 4
// 5

// Length of the array
DECLARE Length : INTEGER
Length ← 5
OUTPUT Length               // Output: 5

# 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

Declare a 2D array with name and number for 3 people

Creates a 3x2 blank array (3 people, each with name and number)

DECLARE NamesAndNumbers : ARRAY[1:3, 1:2] OF STRING

1:3 = 3 rows → one for each person

1:2 = 2 columns → one for name, one for number

OF STRING → both names and phone numbers are stored as strings

NamesANDNumbers = [[None, None], [None, None], [None, None]]

Declare a 2D array called players with name and score assigned for 4 people (Alice, Bob, Charlie & Daisy)

// Declare a 2D array with 4 rows and 2 columns (name and score)

DECLARE players : ARRAY[1:4, 1:2] OF STRING

// Assign values to each player

players[1,1] ← "Alice"

players[1,2] ← "25"

players[2,1] ← "Bob"

players[2,2] ← "30"

players[3,1] ← "Charlie"

players[3,2] ← "22"

players[4,1] ← "Daisy"

players[4,2] ← "28"

# Each player has a name and a score

players = [

["Alice", 25],

["Bob", 30],

["Charlie", 22],

["Daisy", 28]

]

Assignment

Assigning the name Holly to replace the name Charlie

players[3,1] ← "Holly"

players[2][0] = "Holly" # Charlie is at index 2 (third row), name is at index 0

DECLARE Array2D : ARRAY[1:3, 1:3] OF INTEGER
Array2D[1,1] ← 1
Array2D[1,2] ← 2
Array2D[1,3] ← 3
Array2D[2,1] ← 4
Array2D[2,2] ← 5
Array2D[2,3] ← 6
Array2D[3,1] ← 7
Array2D[3,2] ← 8
Array2D[3,3] ← 9

// Accessing elements in the 2D array
OUTPUT Array2D[1,1]       // Output: 1
OUTPUT Array2D[2,3]       // Output: 6

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

DECLARE Row : INTEGER
DECLARE Col : INTEGER
FOR Row ← 1 TO 3
    FOR Col ← 1 TO 3
        OUTPUT Array2D[Row, Col]
    NEXT Col
NEXT Row

for row in array_2d: 
    for item in row: 
        print(item, end=" ") 
    print() # Print a newline after each row