AllCoderThings

Posted on Apr 7

Working with Data in C#: Arrays

#csharp #programming #beginners #dotnet

Originally published at https://allcoderthings.com/en/article/csharp-arrays

In C#, arrays are used to store multiple values of the same type consecutively in memory. Indexing provides fast access to elements. This article provides a detailed introduction from array declarations to multi-dimensional arrays, as well as practical examples using Array class methods.

What is an Array?

An array is a structure where data of the same type is stored in consecutive memory cells. Each element is accessed using an index number. Indexes start at 0.

int[] numbers = new int[5]; // an int array with 5 elements

Declaring Arrays and Default Values

When declaring an array, its size is specified. If no values are assigned, default values are used:

int → 0
bool → false
string → null

string[] names = new string[3];
Console.WriteLine(names[0]); // null

Assigning and Accessing Array Elements (Indexing)

Elements are accessed by index. Since indexes start at 0, the last element is located at Length - 1.

int[] grades = new int[5];
grades[0] = 85;
grades[1] = 90;
grades[2] = 70;
grades[3] = 75;
grades[4] = 60;

Console.WriteLine(grades[1]); // 90
Console.WriteLine(grades[^1]); // 60, This will give last element (Length - 1)

int[] sub_grades = grades[1..4]; // A sub array: 90, 70, 75

grades[5] = 100; // This will throw IndexOutOfRangeException

Assigning or accessing indices outside the array size throws an IndexOutOfRangeException. For example, in array[4], valid indices are 0, 1, 2, 3. Values like -1, 4, or 5 will cause an error. The first element is always accessed with index 0.

Array Initialization Shortcuts

You can assign values directly while creating an array.

int[] numbers = { 10, 20, 30 };
var letters = new char[] { 'A', 'B', 'C' };

Iterating Over Arrays with Loops

for and foreach loops are used to access array elements.

int[] numbers = { 3, 6, 9 };

// with for
for (int i = 0; i < numbers.Length; i++)
    Console.WriteLine(numbers[i]);

// with foreach
foreach (var n in numbers)
    Console.WriteLine(n);

Multi-Dimensional Arrays (2D, 3D)

Multi-dimensional arrays are used to store data in table or matrix form. Elements can be accessed using indexes or iterated with nested loops.

int[,] matrix = new int[2, 3]
{
    {1, 2, 3},
    {4, 5, 6}
};

Console.WriteLine(matrix[1, 2]); // 6

// Iterating with nested for loops
for (int i = 0; i < matrix.GetLength(0); i++) // rows
{
    for (int j = 0; j < matrix.GetLength(1); j++) // columns
    {
        Console.Write(matrix[i, j] + " ");
    }
    Console.WriteLine();
}

// Output:
6
1 2 3 
4 5 6

Jagged Arrays

In jagged arrays, each row can have a different length. This is different from matrices.

int[][] jagged = new int[3][];
jagged[0] = new int[] {1, 2};
jagged[1] = new int[] {3, 4, 5};
jagged[2] = new int[] {6};

Console.WriteLine(jagged[1][2]); // 5

The Array Class and Useful Methods

In C#, all arrays derive from the Array class. Commonly used methods include:

int[] numbers = { 5, 2, 9, 1, 7 };

Array.Sort(numbers);    // Sorting
Array.Reverse(numbers); // Reversing
int index = Array.IndexOf(numbers, 9); // Searching for element

Console.WriteLine(index);

Sample Application: Student Grades

In the following example, students' grades are stored in an array and their average is calculated.

int[] grades = { 80, 70, 95, 60, 100 };

int total = 0;
foreach (var g in grades)
    total += g;

double average = (double)total / grades.Length;
Console.WriteLine($"Average: {average}");

TL;DR

Arrays store values of the same type consecutively in memory.

Indexes start at 0; default values are the type's default.

You can iterate through arrays with for and foreach.

Multi-dimensional and jagged arrays are supported.

The Array class provides useful array methods.

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