What are arrays?

Array stores same-type values together.

Memory sits contiguous. Index starts at 0.

int mark1 = 85;
int mark2 = 90;
int mark3 = 78;
int mark4 = 95;
int mark5 = 88;

// vs

int marks[5] = {85, 90, 78, 95, 88};

Arrays shorten and organize code.

School lockers analogy. Each has a number.

Why do arrays exist?

• Grouping similar data together
• Making data easier to process
• Reducing repetitive code
• Simplifying loops and algorithms

Real-world use cases

• Student mark management systems
• Inventory management
• Banking applications
• Game development
• Sensor data collection
• Image processing
• Mathematical computations
• Searching and sorting algorithms

Array declaration

data_type array_name[size];

int numbers[5];

Array initialization

data_type array_name[size] = {value1, value2, ...};

int numbers[5] = {10, 20, 30, 40, 50};

Accessing array elements

numbers[0]
numbers[1]
numbers[2]

• First element: index 0
• Last element: size - 1

Modifying array elements

numbers[2] = 100;

Traversing an array

Traversal visits every element in order.

for loop is most common for traversal.

Array size

sizeof finds an array's element count.

int size = sizeof(numbers) / sizeof(numbers[0]);

Works only for compile-time known sizes.

Multidimensional arrays

Stores data in rows and columns.

int matrix[2][3];

• Tables
• Matrices
• Game boards
• Grid-based problems

Example 1: Declare and display an array

#include <iostream>
using namespace std;

int main()
{
    int numbers[5] = {10, 20, 30, 40, 50};

    cout << numbers[0] << '\n';
    cout << numbers[4] << '\n';

    return 0;
}

Example 2: Read array elements

#include <iostream>
using namespace std;

int main()
{
    int marks[5];

    cout << "Enter 5 marks:\n";

    for (int i = 0; i < 5; i++)
    {
        cin >> marks[i];
    }

    cout << "\nMarks:\n";

    for (int i = 0; i < 5; i++)
    {
        cout << marks[i] << '\n';
    }

    return 0;
}

Example 3: Find the largest element

#include <iostream>
using namespace std;

int main()
{
    int numbers[5] = {12, 45, 8, 67, 23};

    int largest = numbers[0];

    for (int i = 1; i < 5; i++)
    {
        if (numbers[i] > largest)
        {
            largest = numbers[i];
        }
    }

    cout << "Largest = " << largest;

    return 0;
}

Example 4: Calculate average

#include <iostream>
using namespace std;

int main()
{
    int marks[5] = {80, 75, 90, 85, 95};

    int sum = 0;

    for (int i = 0; i < 5; i++)
    {
        sum += marks[i];
    }

    double average = static_cast<double>(sum) / 5;

    cout << "Average = " << average;

    return 0;
}

Example 5: Two-dimensional array

#include <iostream>
using namespace std;

int main()
{
    int matrix[2][3] =
    {
        {1, 2, 3},
        {4, 5, 6}
    };

    for (int row = 0; row < 2; row++)
    {
        for (int col = 0; col < 3; col++)
        {
            cout << matrix[row][col] << " ";
        }

        cout << '\n';
    }

    return 0;
}

Common mistakes and pitfalls

• Accessing numbers[5] in 5-element array. Fix: use index 4
• Forgetting array size. Fix: specify or init correctly
• Using negative index. Fix: start from 0
• Traversing past array size. Fix: stop at size - 1
• Assuming arrays auto-resize. Fix: use std::vector

// Wrong
int numbers[5];
cout << numbers[5];

// Correct
int numbers[5];
cout << numbers[4];

Best practices

• Use meaningful array names
• Validate indices before accessing
• Use loops instead of repetitive statements
• Avoid hardcoding sizes everywhere
• Use std::vector for unknown sizes
• Initialize arrays before use

When not to use this

• Element count changes at runtime
• Frequent insertion or deletion needed
• You need automatic memory management
• You need sorting or dynamic resizing built in

Prefer std::vector in these cases.

Summary

• Arrays store same-type values
• Memory is contiguous
• Indexing starts from 0
• Arrays have fixed size
• Loops traverse arrays commonly
• 2D arrays hold rows and columns
• Avoid out-of-bounds access
• Use std::vector for dynamic sizing

Frequently asked questions

What is an array in C++?

Same-type elements stored contiguously, indexed.

Why do array indices start from 0?

Index is offset from first element in memory.

Can I change array size after declaring it?

No. Use std::vector for resizable data.

What is a multidimensional array?

Array of arrays. Common example: rows and columns.

What happens if I access an out-of-bounds element?

Undefined behavior. Crashes or wrong output possible.