Mastering C# Arrays: Declaration, Initialization, and Operations

Mastering C# Arrays

Discover how to declare, initialize, and work with arrays in C#. Practical code examples, looping techniques, and LINQ operations are covered.

An array stores a fixed-size sequence of elements of the same type. For example, instead of five separate variables for student ages, a single array is sufficient.

---

1. Declaring an Array in C#

Use the following syntax to declare an array:

datatype[] arrayName;

• datatype – e.g., int, string, char, etc.
• arrayName – a valid identifier.

Example:

int[] age;

Here, age can hold integer values.

Determining the array size

Allocate memory to set the number of elements:

// declare an array
int[] age;

// allocate memory for 5 elements
age = new int[5];

Alternatively, declare and allocate in one statement:

int[] age = new int[5];

---

2. Initializing an Array

Arrays can be initialized during declaration:

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

The compiler infers the size from the initializer.

Individual elements can also be set after declaration:

// declare an array
int[] age = new int[5];

// initialize elements
age[0] = 12;
age[1] = 4;
age[2] = 5;
// …

• Array indices start at 0.
• A 5‑element array has indices 0‑4.

---

3. Accessing Elements

Retrieve an element by its index:

// third element
array[2];
// fifth element
array[4];

• array[2] returns the third element.
• array[4] returns the fifth element.

---

Example: Accessing Array Elements

using System;

namespace AccessArray {
  class Program  {
    static void Main(string[] args) {

      // create an array
      int[] numbers = {1, 2, 3};

      // access first element
      Console.WriteLine("Element at index 0 : " + numbers[0]);

      // access second element
      Console.WriteLine("Element at index 1 : " + numbers[1]);

      // access third element
      Console.WriteLine("Element at index 2 : " + numbers[2]);

      Console.ReadLine();

    }
  }
}

Output

Element at index 0 : 1
Element at index 1 : 2
Element at index 2 : 3

---

4. Modifying Elements

Change an element by assigning a new value to its index:

using System;

namespace ChangeArray {
  class Program {
    static void Main(string[] args) {

      // create an array
      int[] numbers = {1, 2, 3};

      Console.WriteLine("Old Value at index 0: " + numbers[0]);

      // update value
      numbers[0] = 11;

      Console.WriteLine("New Value at index 0: " + numbers[0]);

      Console.ReadLine();
    }
  }
}

Output

Old Value at index 0: 1
New Value at index 0: 11

---

5. Iterating with Loops

Use for or foreach to traverse an array.

For Loop Example

using System;

namespace AccessArrayFor {
  class Program {
    static void Main(string[] args) {

      int[] numbers = { 1, 2, 3};
      
      for(int i=0; i < numbers.Length; i++) {
        Console.WriteLine("Element at index " + i + ": " + numbers[i]);
      }

      Console.ReadLine();
    }
  }
}

Output

Element at index 0: 1
Element at index 1: 2
Element at index 2: 3

Use numbers.Length to obtain the array size.

Foreach Loop Example

using System;

namespace AccessArrayForeach {
  class Program {
    static void Main(string[] args) {
      int[] numbers = {1, 2, 3};

      Console.WriteLine("Array Elements: ");

      foreach(int num in numbers) {
        Console.WriteLine(num);
      }

      Console.ReadLine();
    }
  }
}

Output

Array Elements:
1
2
3

---

6. Array Operations with System.Linq

The System.Linq namespace offers powerful methods for array manipulation.

Finding Minimum and Maximum

using System;
using System.Linq;

namespace ArrayMinMax {
  class Program  {
    static void Main(string[] args) {

      int[] numbers = {51, 1, 3, 4, 98};

      Console.WriteLine("Smallest Element: " + numbers.Min());
      Console.WriteLine("Largest Element: " + numbers.Max());

      Console.ReadLine();
    }
  }
}

Output

Smallest Element: 1
Largest Element: 98

Calculating the Average

using System;
using System.Linq;

namespace ArrayFunction {
  class Program  {
    static void Main(string[] args) {

      int[] numbers = {30, 31, 94, 86, 55};
      
      float sum = numbers.Sum();
      int count = numbers.Count();
      float average = sum / count;

      Console.WriteLine("Average : " + average);
      Console.WriteLine("Average using Average() : " + numbers.Average());

      Console.ReadLine();
    }
  }
}

Output

Average : 59.2
Average using Average() : 59.2

Note: Include using System.Linq; to access Min, Max, Sum, Count, and Average methods.