How to set a value to the element at the specified position in the one-dimensional array in C#

In C#, you can set a value to an element at a specific position in a one-dimensional array using the array indexing operator []. Array indexing in C# is zero-based, meaning the first element is at index 0, the second at index 1, and so on.

Syntax

Following is the syntax for setting a value to an array element at a specified position −

arrayName[index] = value;

Where index is the position (starting from 0) and value is the new value to be assigned.

Using Array Index Assignment

First, declare and initialize an array −

int[] arr = new int[] {55, 66, 88, 99, 111, 122, 133};

To set an element at position 2 (third element) −

arr[2] = 77;

Example

using System;

namespace Program {
    public class Demo {
        public static void Main(string[] args) {
            int[] p = new int[] {55, 66, 88, 99, 111, 122, 133};
            int j;

            Console.WriteLine("Initial Array......");
            for (j = 0; j < p.Length; j++) {
                Console.WriteLine("arr[{0}] = {1}", j, p[j]);
            }

            // set new element at index 2
            p[2] = 77;

            Console.WriteLine("New Array......");
            for (j = 0; j < p.Length; j++) {
                Console.WriteLine("arr[{0}] = {1}", j, p[j]);
            }
        }
    }
}

The output of the above code is −

Initial Array......
arr[0] = 55
arr[1] = 66
arr[2] = 88
arr[3] = 99
arr[4] = 111
arr[5] = 122
arr[6] = 133
New Array......
arr[0] = 55
arr[1] = 66
arr[2] = 77
arr[3] = 99
arr[4] = 111
arr[5] = 122
arr[6] = 133

Setting Multiple Elements

Example

using System;

class Program {
    public static void Main() {
        string[] fruits = {"Apple", "Banana", "Cherry", "Date"};
        
        Console.WriteLine("Original Array:");
        for (int i = 0; i < fruits.Length; i++) {
            Console.WriteLine("fruits[{0}] = {1}", i, fruits[i]);
        }
        
        // Set values at different positions
        fruits[1] = "Blueberry";
        fruits[3] = "Dragon Fruit";
        
        Console.WriteLine("\nModified Array:");
        for (int i = 0; i < fruits.Length; i++) {
            Console.WriteLine("fruits[{0}] = {1}", i, fruits[i]);
        }
    }
}

The output of the above code is −

Original Array:
fruits[0] = Apple
fruits[1] = Banana
fruits[2] = Cherry
fruits[3] = Date

Modified Array:
fruits[0] = Apple
fruits[1] = Blueberry
fruits[2] = Cherry
fruits[3] = Dragon Fruit

Key Rules

• Array indices are zero-based − the first element is at index 0.

• The index must be within the valid range: 0 ≤ index < array.Length.

• Accessing an invalid index throws an IndexOutOfRangeException.

• The assigned value must match the array's data type.

Conclusion

Setting values in C# arrays is straightforward using the indexing operator arrayName[index] = value. Remember that array indices start from 0, and always ensure the index is within the valid range to avoid runtime exceptions.