Are arrays zero indexed in C#?

Yes, arrays are zero-indexed in C#. This means the first element of an array is stored at index 0, the second element at index 1, and so on. The relationship between array length and indexing follows a consistent pattern.

Array Length vs Index Range

• If the array is empty, it has zero elements and length 0.

• If the array has one element at index 0, then it has length 1.

• If the array has two elements at indexes 0 and 1, then it has length 2.

• If the array has three elements at indexes 0, 1, and 2, then it has length 3.

Syntax

Arrays in C# are accessed using square brackets with zero-based indexing −

dataType[] arrayName = new dataType[size];
arrayName[0] = value;  // first element
arrayName[1] = value;  // second element
arrayName[size-1] = value;  // last element

Example

The following example demonstrates zero-based indexing by populating and displaying array elements −

using System;

namespace ArrayApplication {
   class MyArray {
      static void Main(string[] args) {
         int[] n = new int[5];
         int i, j;
         
         /* begins from index 0 */
         for (i = 0; i < 5; i++) {
            n[i] = i + 5;
         }
         
         for (j = 0; j < 5; j++) {
            Console.WriteLine("Element[{0}] = {1}", j, n[j]);
         }
      }
   }
}

The output of the above code is −

Element[0] = 5
Element[1] = 6
Element[2] = 7
Element[3] = 8
Element[4] = 9

Accessing First and Last Elements

Here's an example showing how to access the first and last elements of an array −

using System;

class Program {
   static void Main() {
      string[] colors = {"Red", "Green", "Blue", "Yellow", "Orange"};
      
      Console.WriteLine("Array length: " + colors.Length);
      Console.WriteLine("First element (index 0): " + colors[0]);
      Console.WriteLine("Last element (index {0}): {1}", colors.Length - 1, colors[colors.Length - 1]);
      
      // Display all elements with their indexes
      for (int i = 0; i < colors.Length; i++) {
         Console.WriteLine("colors[{0}] = {1}", i, colors[i]);
      }
   }
}

The output of the above code is −

Array length: 5
First element (index 0): Red
Last element (index 4): Orange
colors[0] = Red
colors[1] = Green
colors[2] = Blue
colors[3] = Yellow
colors[4] = Orange

Key Points

• The first element is always at index 0.

• The last element is at index Length - 1.

• Accessing an index outside the range [0, Length-1] throws an IndexOutOfRangeException.

• Array length is always one more than the highest valid index.

Conclusion

Arrays in C# are zero-indexed, meaning the first element is at index 0 and the last element is at index Length-1. Understanding this indexing system is fundamental for working with arrays and avoiding common off-by-one errors in C# programming.