Arrays and Records

This lesson covers arrays and records — two fundamental static data structures used extensively in A-Level Computer Science. Arrays store collections of elements of the same type, while records group related data of different types.

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Arrays

An array is a static data structure that stores a fixed number of elements of the same data type in contiguous memory locations. Each element is accessed using an index (a numerical position).

Key Properties

Property	Description
Fixed size	The size is set when the array is created and cannot change.
Homogeneous	All elements must be of the same data type.
Contiguous memory	Elements are stored next to each other in memory.
Indexed access	Any element can be accessed directly using its index in O(1) time.
Zero-based indexing	In most languages, the first element is at index 0.

Pseudocode

DECLARE names: ARRAY[0..4] OF STRING
names[0] = "Alice"
names[1] = "Bob"
names[2] = "Charlie"

// Traverse the array
FOR i = 0 TO 4
    OUTPUT names[i]
NEXT i

Python

# Python lists are dynamic, but are often used to demonstrate array concepts
names = ["Alice", "Bob", "Charlie", "Diana", "Eve"]

# Access by index
print(names[0])    # Alice
print(names[2])    # Charlie

# Traverse the array
for name in names:
    print(name)

# Access with index
for i in range(len(names)):
    print(f"Index {i}: {names[i]}")

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One-Dimensional Arrays

A one-dimensional (1D) array is a linear list of elements, like a single row.

Index:  [0]    [1]    [2]    [3]    [4]
Values:  10     20     30     40     50

Common Operations

Operation	Description	Time Complexity
Access	Read/write element at index i	O(1)
Search (linear)	Find an element by value	O(n)
Search (binary)	Find in sorted array	O(log n)
Insert	Add at a specific position (shifting required)	O(n)
Delete	Remove from a specific position (shifting required)	O(n)

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Two-Dimensional Arrays

A two-dimensional (2D) array is an array of arrays — a grid or table with rows and columns.

         Col 0   Col 1   Col 2
Row 0  [  10  ,   20  ,   30  ]
Row 1  [  40  ,   50  ,   60  ]
Row 2  [  70  ,   80  ,   90  ]

Pseudocode

DECLARE grid: ARRAY[0..2, 0..2] OF INTEGER
grid[0][0] = 10
grid[1][2] = 60

// Traverse a 2D array
FOR row = 0 TO 2
    FOR col = 0 TO 2
        OUTPUT grid[row][col]
    NEXT col
NEXT row

Python

grid = [
    [10, 20, 30],
    [40, 50, 60],
    [70, 80, 90]
]

# Access element at row 1, column 2
print(grid[1][2])  # 60

# Traverse the 2D array
for row in range(len(grid)):
    for col in range(len(grid[row])):
        print(f"grid[{row}][{col}] = {grid[row][col]}")