Arrays

An array is a fixed-size data structure that stores multiple items of the same data type in a sequence. Each item is stored at a specific index position, with the first element at index 0.

Key features of arrays

• Fixed size — set when declared, cannot change during execution
• All elements must be the same data type
• Elements accessed by index: nums[0], nums[1], etc.
• Efficient for random access — accessing any element is O(1)

Example (Edexcel pseudocode)

Declare an array of 5 integers:

scores ← [10, 20, 30, 40, 50]
OUTPUT scores[0]    // Outputs 10
scores[2] ← 99     // Changes index 2 from 30 to 99

Iterating over an array

FOR i ← 0 TO 4
    OUTPUT scores[i]
NEXT i

Two-Dimensional Arrays

A 2D array is like a table with rows and columns. Each element is accessed using two indices: array[row][col].

grid ← [[1,2,3],[4,5,6],[7,8,9]]
OUTPUT grid[1][2]   // Row 1, Column 2 → outputs 6

Lists vs Arrays

In some languages, a list is a dynamic structure — it can grow and shrink. In Edexcel 1CP2, the term "array" usually refers to the fixed-size structure. The differences are: