Module 6: Arrays in C++

An array is a collection of elements of the same data type stored in contiguous memory locations. Arrays allow you to store multiple values using a single variable name and access each element using its index.

Example:

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1int marks[5] = {80, 75, 90, 85, 95};

1. One-Dimensional Array

A one-dimensional (1D) array stores elements in a single row.

Syntax

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1dataType arrayName[size];

Example

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1#include <iostream>
2using namespace std;
3
4int main()
5{
6    int marks[5] = {80, 75, 90, 85, 95};
7
8    for (int i = 0; i < 5; i++)
9    {
10        cout << marks[i] << " ";
11    }
12
13    return 0;
14}

Output

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180 75 90 85 95

2. Two-Dimensional Array

A two-dimensional (2D) array represents data in rows and columns, similar to a table or matrix.

Syntax

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1dataType arrayName[rows][columns];

Example

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1#include <iostream>
2using namespace std;
3
4int main()
5{
6    int matrix[2][3] =
7    {
8        {1, 2, 3},
9        {4, 5, 6}
10    };
11
12    for (int i = 0; i < 2; i++)
13    {
14        for (int j = 0; j < 3; j++)
15        {
16            cout << matrix[i][j] << " ";
17        }
18        cout << endl;
19    }
20
21    return 0;
22}

Output

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11 2 3
24 5 6

3. Three-Dimensional Array

A three-dimensional (3D) array stores data in multiple layers. It is commonly used in graphics, scientific computing, and simulations.

Syntax

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1dataType arrayName[x][y][z];

Example

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1#include <iostream>
2using namespace std;
3
4int main()
5{
6    int arr[2][2][2] =
7    {
8        {
9            {1, 2},
10            {3, 4}
11        },
12        {
13            {5, 6},
14            {7, 8}
15        }
16    };
17
18    cout << arr[1][0][1];
19
20    return 0;
21}

Output

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16

4. Passing Arrays to Functions

Arrays can be passed to functions for processing without copying all elements.

Example

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1#include <iostream>
2using namespace std;
3
4void display(int arr[], int size)
5{
6    for (int i = 0; i < size; i++)
7    {
8        cout << arr[i] << " ";
9    }
10}
11
12int main()
13{
14    int numbers[] = {10, 20, 30, 40, 50};
15
16    display(numbers, 5);
17
18    return 0;
19}

Output

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110 20 30 40 50

5. Searching Arrays

Searching is the process of finding a specific element in an array.

Linear Search

Linear search checks each element one by one.

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1#include <iostream>
2using namespace std;
3
4int main()
5{
6    int arr[] = {10, 20, 30, 40, 50};
7    int key = 30;
8    bool found = false;
9
10    for (int i = 0; i < 5; i++)
11    {
12        if (arr[i] == key)
13        {
14            found = true;
15            break;
16        }
17    }
18
19    if (found)
20        cout << "Element Found";
21    else
22        cout << "Element Not Found";
23
24    return 0;
25}

Output

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1Element Found

Note: Binary Search is faster than Linear Search but requires the array to be sorted.

6. Sorting Arrays

Sorting arranges array elements in ascending or descending order.

Bubble Sort

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1#include <iostream>
2using namespace std;
3
4int main()
5{
6    int arr[] = {5, 2, 8, 1, 4};
7    int n = 5;
8
9    for (int i = 0; i < n - 1; i++)
10    {
11        for (int j = 0; j < n - i - 1; j++)
12        {
13            if (arr[j] > arr[j + 1])
14            {
15                swap(arr[j], arr[j + 1]);
16            }
17        }
18    }
19
20    for (int i = 0; i < n; i++)
21    {
22        cout << arr[i] << " ";
23    }
24
25    return 0;
26}

Output

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11 2 4 5 8

Best Practices

• Always initialize arrays before using them.
• Ensure indices remain within array bounds.
• Use loops to traverse arrays efficiently.
• Pass array size when sending arrays to functions.
• Use standard library algorithms like std::sort() for better performance in real-world applications.

Common Mistakes

Accessing an Invalid Index

❌ Incorrect

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1int arr[5];
2
3cout << arr[5];

Array indices range from 0 to 4.

✅ Correct

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1cout << arr[4];

Forgetting Array Size

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1int numbers[5];

Only five elements can be stored.

Practice Problems

1. Find the largest element in an array.
2. Find the smallest element in an array.
3. Calculate the sum and average of array elements.
4. Reverse an array.
5. Search for an element using Linear Search.
6. Implement Binary Search on a sorted array.
7. Sort an array using Bubble Sort.
8. Sort an array using Selection Sort.
9. Add two matrices.
10. Transpose a matrix.

Interview Questions

1. What is an array in C++?
2. What is the difference between 1D, 2D, and 3D arrays?
3. How are arrays passed to functions?
4. What is the difference between Linear Search and Binary Search?
5. Which sorting algorithm is implemented above?
6. What happens if you access an array index out of bounds?
7. What is the time complexity of Bubble Sort?
8. When should you use multidimensional arrays?

Summary

In this module, you learned:

• What arrays are and why they are used.
• How to create and use one-dimensional, two-dimensional, and three-dimensional arrays.
• How to pass arrays to functions.
• How Linear Search works to find elements.
• How Bubble Sort arranges array elements in order.
• Common mistakes, best practices, and practical exercises.

In the next module, you'll learn Pointers in C++, including pointer declaration, pointer arithmetic, pointers and arrays, pointers to functions, dynamic memory allocation (new and delete), smart pointers, and memory management.