Skip to main content

C# Arrays

Arrays are one of the fundamental data structures in C# that allow you to store multiple values of the same type in a single variable. Whether you're storing a list of numbers, names, or any collection of similar items, arrays provide a simple and efficient way to manage this data.

What is an Array?​

An array in C# is a collection of elements of the same data type, stored at contiguous memory locations. Think of it as a container that can hold a fixed number of items where each item has a specific position (index).

Key characteristics of arrays in C#:

  • Fixed size (cannot change after creation)
  • Zero-indexed (positions start from 0)
  • Can be single or multi-dimensional
  • Store elements of the same data type

Creating Arrays​

There are several ways to create arrays in C#:

1. Declaring and Initializing in One Step​

csharp
// Declare and initialize with values
int[] numbers = { 1, 2, 3, 4, 5 };

// Declare and initialize a string array
string[] days = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" };

2. Declare First, Initialize Later​

csharp
// Declare an array of integers with size 5
int[] scores = new int[5];

// Initialize individual elements
scores[0] = 85;
scores[1] = 92;
scores[2] = 78;
scores[3] = 95;
scores[4] = 88;

3. Alternative Syntax​

csharp
// Another valid syntax
int[] points = new int[] { 10, 20, 30, 40, 50 };

Accessing Array Elements​

To access elements in an array, use the index position inside square brackets:

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

// Access an element
Console.WriteLine($"The first element is: {numbers[0]}");  // Output: The first element is: 10
Console.WriteLine($"The third element is: {numbers[2]}");  // Output: The third element is: 30

// Modify an element
numbers[1] = 25;
Console.WriteLine($"The updated second element is: {numbers[1]}");  // Output: The updated second element is: 25

Array Length​

You can get the size of an array using the Length property:

csharp
int[] numbers = { 10, 20, 30, 40, 50 };
Console.WriteLine($"The array contains {numbers.Length} elements");  // Output: The array contains 5 elements

Iterating Through Arrays​

There are several ways to iterate through an array:

Using a for loop​

csharp
int[] scores = { 85, 92, 78, 95, 88 };

Console.WriteLine("Scores using for loop:");
for (int i = 0; i < scores.Length; i++)
{
    Console.WriteLine($"Score {i+1}: {scores[i]}");
}

// Output:
// Scores using for loop:
// Score 1: 85
// Score 2: 92
// Score 3: 78
// Score 4: 95
// Score 5: 88

Using a foreach loop​

csharp
string[] fruits = { "Apple", "Banana", "Cherry", "Date", "Elderberry" };

Console.WriteLine("Fruits using foreach loop:");
foreach (string fruit in fruits)
{
    Console.WriteLine(fruit);
}

// Output:
// Fruits using foreach loop:
// Apple
// Banana
// Cherry
// Date
// Elderberry

Multi-dimensional Arrays​

C# supports multi-dimensional arrays, which can be either rectangular or jagged.

Rectangular Arrays (2D)​

csharp
// Creating a 2D array (3 rows, 4 columns)
int[,] matrix = new int[3, 4] {
    { 1, 2, 3, 4 },
    { 5, 6, 7, 8 },
    { 9, 10, 11, 12 }
};

// Accessing elements
Console.WriteLine(matrix[1, 2]);  // Output: 7 (row 1, column 2)

// Iterating through a 2D array
for (int i = 0; i < matrix.GetLength(0); i++)
{
    for (int j = 0; j < matrix.GetLength(1); j++)
    {
        Console.Write($"{matrix[i, j]}\t");
    }
    Console.WriteLine();
}

// Output:
// 1    2    3    4
// 5    6    7    8
// 9    10   11   12

Jagged Arrays (Arrays of Arrays)​

csharp
// Declare a jagged array (array of arrays)
int[][] jaggedArray = new int[3][];

// Initialize the arrays
jaggedArray[0] = new int[] { 1, 2, 3 };
jaggedArray[1] = new int[] { 4, 5, 6, 7 };
jaggedArray[2] = new int[] { 8, 9 };

// Access elements
Console.WriteLine(jaggedArray[1][2]);  // Output: 6

// Iterate through a jagged array
for (int i = 0; i < jaggedArray.Length; i++)
{
    Console.Write($"Row {i}: ");
    for (int j = 0; j < jaggedArray[i].Length; j++)
    {
        Console.Write($"{jaggedArray[i][j]} ");
    }
    Console.WriteLine();
}

// Output:
// Row 0: 1 2 3
// Row 1: 4 5 6 7
// Row 2: 8 9

Common Array Operations​

Copying Arrays​

csharp
int[] originalArray = { 1, 2, 3, 4, 5 };

// Method 1: Using Array.Copy
int[] copy1 = new int[originalArray.Length];
Array.Copy(originalArray, copy1, originalArray.Length);

// Method 2: Using Clone()
int[] copy2 = (int[])originalArray.Clone();

// Method 3: Using CopyTo()
int[] copy3 = new int[originalArray.Length];
originalArray.CopyTo(copy3, 0);

Sorting Arrays​

csharp
int[] unsortedNumbers = { 5, 2, 8, 3, 1, 6 };

// Sort the array
Array.Sort(unsortedNumbers);

Console.WriteLine("Sorted array:");
foreach (int num in unsortedNumbers)
{
    Console.Write($"{num} ");
}
// Output: Sorted array: 1 2 3 5 6 8

Searching in Arrays​

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

// Binary search (array must be sorted)
int index = Array.BinarySearch(numbers, 30);
Console.WriteLine($"30 found at index: {index}");  // Output: 30 found at index: 2

// Find the index of the first occurrence
int firstIndex = Array.IndexOf(numbers, 40);
Console.WriteLine($"First occurrence of 40 is at index: {firstIndex}");  // Output: First occurrence of 40 is at index: 3

// Check if array contains a value
bool contains = Array.Exists(numbers, element => element == 20);
Console.WriteLine($"Array contains 20: {contains}");  // Output: Array contains 20: True

Resizing Arrays​

Since arrays have a fixed size, to "resize" an array, you actually create a new array and copy the elements:

csharp
int[] original = { 1, 2, 3 };

// Resize to a larger array
Array.Resize(ref original, 5);
original[3] = 4;
original[4] = 5;

Console.WriteLine("Resized array:");
foreach (int num in original)
{
    Console.Write($"{num} ");
}
// Output: Resized array: 1 2 3 4 5

// Resize to a smaller array
Array.Resize(ref original, 2);
Console.WriteLine("\nTruncated array:");
foreach (int num in original)
{
    Console.Write($"{num} ");
}
// Output: Truncated array: 1 2

Practical Examples​

Example 1: Calculate Average Temperature​

csharp
double[] weeklyTemperatures = { 72.5, 75.0, 68.3, 70.1, 74.2, 79.8, 76.5 };

// Calculate the average temperature
double sum = 0;
foreach (double temp in weeklyTemperatures)
{
    sum += temp;
}
double average = sum / weeklyTemperatures.Length;

Console.WriteLine($"Average weekly temperature: {average:F1}°F");
// Output: Average weekly temperature: 73.8°F

Example 2: Student Grade Tracker​

csharp
string[] studentNames = { "Alice", "Bob", "Charlie", "Diana", "Evan" };
int[] scores = { 92, 85, 78, 95, 88 };

// Display student grades
Console.WriteLine("Student Grades:");
for (int i = 0; i < studentNames.Length; i++)
{
    string grade;
    if (scores[i] >= 90) grade = "A";
    else if (scores[i] >= 80) grade = "B";
    else if (scores[i] >= 70) grade = "C";
    else if (scores[i] >= 60) grade = "D";
    else grade = "F";
    
    Console.WriteLine($"{studentNames[i]}: {scores[i]} ({grade})");
}

// Find highest scorer
int highestScore = scores[0];
int highestIndex = 0;
for (int i = 1; i < scores.Length; i++)
{
    if (scores[i] > highestScore)
    {
        highestScore = scores[i];
        highestIndex = i;
    }
}

Console.WriteLine($"\nHighest score: {studentNames[highestIndex]} with {highestScore}");

// Output:
// Student Grades:
// Alice: 92 (A)
// Bob: 85 (B)
// Charlie: 78 (C)
// Diana: 95 (A)
// Evan: 88 (B)
//
// Highest score: Diana with 95

Example 3: Basic Inventory System​

csharp
// Product inventory example
string[] productNames = new string[5];
double[] prices = new double[5];
int[] quantities = new int[5];

// Initialize with some products
productNames[0] = "Laptop";
prices[0] = 1200.00;
quantities[0] = 5;

productNames[1] = "Monitor";
prices[1] = 350.00;
quantities[1] = 8;

productNames[2] = "Keyboard";
prices[2] = 80.00;
quantities[2] = 12;

// Display inventory
Console.WriteLine("Current Inventory:");
Console.WriteLine("--------------------------------");
Console.WriteLine("Product\tPrice\tQuantity\tValue");
Console.WriteLine("--------------------------------");

double totalValue = 0;
for (int i = 0; i < productNames.Length; i++)
{
    if (productNames[i] != null)
    {
        double value = prices[i] * quantities[i];
        totalValue += value;
        Console.WriteLine($"{productNames[i]}\t${prices[i]}\t{quantities[i]}\t\t${value}");
    }
}

Console.WriteLine("--------------------------------");
Console.WriteLine($"Total Inventory Value: ${totalValue}");

// Output:
// Current Inventory:
// --------------------------------
// Product Price   Quantity        Value
// --------------------------------
// Laptop  $1200   5               $6000
// Monitor $350    8               $2800
// Keyboard        $80     12              $960
// --------------------------------
// Total Inventory Value: $9760

Common Pitfalls and Best Practices​

IndexOutOfRangeException​

One of the most common exceptions when working with arrays is the IndexOutOfRangeException, which occurs when you try to access an index that doesn't exist:

csharp
int[] numbers = { 1, 2, 3 };
// This will throw an IndexOutOfRangeException:
// Console.WriteLine(numbers[3]); // Index 3 is out of range

Always ensure you're accessing valid indices by checking against the array's length.

Arrays vs. Other Collections​

Arrays are great for fixed-size collections, but if you need a dynamic collection that can resize, consider using:

  • List<T> for a resizable array
  • Dictionary<TKey, TValue> for key-value pairs
  • Other specialized collections in the System.Collections.Generic namespace

Memory Considerations​

Large arrays are allocated on the heap rather than the stack, which can impact performance for very large arrays.

Summary​

Arrays in C# provide a powerful way to work with collections of data of the same type:

  • They have a fixed size defined when created
  • Elements are accessed by index (starting at 0)
  • Arrays can be single or multi-dimensional
  • Common operations include sorting, searching, and iterating
  • Arrays are perfect for fixed-size collections of data

Despite the emergence of more dynamic collection types, arrays remain fundamental in C# programming and understanding them thoroughly is essential for any C# developer.

Exercises​

To strengthen your understanding of C# arrays, try these exercises:

  1. Write a program to find the second largest element in an array
  2. Create a program that merges two sorted arrays into a single sorted array
  3. Implement a program to remove duplicates from an array
  4. Write a program that rotates an array to the right by k steps
  5. Create a basic tic-tac-toe game using a 2D array to represent the board

Additional Resources​


If you spot any mistakes on this website, please let me know at [email protected]. I’d greatly appreciate your feedback! :)