Arrays (Copy)

IGCSE / O Level Computer Science Cheat Sheet
Topic: 8.2 Arrays

📚 What is an Array?

• An array is a collection of elements (values) stored under one name, where each element is accessed by an index.

🔢 One-Dimensional (1D) Arrays

• Stores a list of items in a single row or column
• Index starts at 0 or 1 (depends on the language)

Declaration Example (Pseudocode):

DECLARE marks[5] AS INTEGER

Accessing Elements:

marks[0] ← 90      // Store value
OUTPUT marks[0]    // Retrieve value

🧮 Using Loops with 1D Arrays

FOR i ← 0 TO 4
    INPUT marks[i]
NEXT i

sum ← 0
FOR i ← 0 TO 4
    sum ← sum + marks[i]
NEXT i

🧩 Two-Dimensional (2D) Arrays

• Stores data in rows and columns
• Often visualized as a grid or table

Declaration Example:

DECLARE grid[3][4] AS INTEGER

Accessing Elements:

grid[0][2] ← 5
OUTPUT grid[0][2]

🔁 Nested Iteration for 2D Arrays

FOR row ← 0 TO 2
    FOR col ← 0 TO 3
        INPUT grid[row][col]
    NEXT col
NEXT row

🎯 When to Use Arrays

• When handling lists of similar data (e.g. scores, names)
• When looping through items
• For storing tabular (2D) data

⚙️ Key Operations

📌 Important Notes

• Array indexes are fixed-size
• Cannot store mixed data types (e.g. integers and strings in same array)
• Index out of range errors occur if you access an invalid position