System.IndexOutOfRangeException – Index was outside the bounds of the array

The System.IndexOutOfRangeException – Index was outside the bounds of the array is a runtime exception in C# that occurs when you try to access an array or collection with an index that is outside its valid range. This typically happens when:

1. You use an index that is negative or greater than or equal to the length of the array or collection.
2. You iterate over an array or collection incorrectly.
3. You access an element of a multidimensional array with invalid indices.

Here’s how you can troubleshoot and fix this issue:

---

1. Check Array Bounds

• Ensure that the index you are using is within the valid range of the array or collection. Example:

   int[] numbers = { 1, 2, 3 };
   int value = numbers[3]; // Error: Index 3 is out of bounds

Fix:

   int[] numbers = { 1, 2, 3 };
   int value = numbers[2]; // Correct: Index 2 is within bounds

---

2. Use for Loops Correctly

• When iterating over an array or collection, ensure that the loop condition is correct. Example:

   int[] numbers = { 1, 2, 3 };
   for (int i = 0; i <= numbers.Length; i++) // Error: 'i <= numbers.Length' is out of bounds
   {
       Console.WriteLine(numbers[i]);
   }

Fix:

   int[] numbers = { 1, 2, 3 };
   for (int i = 0; i < numbers.Length; i++) // Correct: 'i < numbers.Length'
   {
       Console.WriteLine(numbers[i]);
   }

---

3. Check Multidimensional Arrays

• When working with multidimensional arrays, ensure that all indices are within bounds. Example:

   int[,] matrix = new int[2, 2];
   int value = matrix[2, 2]; // Error: Indices (2, 2) are out of bounds

Fix:

   int[,] matrix = new int[2, 2];
   int value = matrix[1, 1]; // Correct: Indices (1, 1) are within bounds

---

4. Use foreach Loops

• Use foreach loops to avoid manual index management and prevent out-of-bounds errors. Example:

   int[] numbers = { 1, 2, 3 };
   foreach (int number in numbers) // No need to manage indices
   {
       Console.WriteLine(number);
   }

---

5. Check for Empty Collections

• Ensure that the collection is not empty before accessing its elements. Example:

   List<int> numbers = new List<int>();
   int value = numbers[0]; // Error: Collection is empty

Fix:

   List<int> numbers = new List<int> { 1, 2, 3 };
   if (numbers.Count > 0)
   {
       int value = numbers[0]; // Correct: Collection is not empty
   }

---

Example of Correct Code

using System;
using System.Collections.Generic;

public class Program
{
    public static void Main(string[] args)
    {
        // Example 1: Check array bounds
        int[] numbers = { 1, 2, 3 };
        Console.WriteLine(numbers[2]); // Output: 3

        // Example 2: Use 'for' loops correctly
        for (int i = 0; i < numbers.Length; i++)
        {
            Console.WriteLine(numbers[i]); // Output: 1, 2, 3
        }

        // Example 3: Check multidimensional arrays
        int[,] matrix = new int[2, 2];
        matrix[1, 1] = 10;
        Console.WriteLine(matrix[1, 1]); // Output: 10

        // Example 4: Use 'foreach' loops
        foreach (int number in numbers)
        {
            Console.WriteLine(number); // Output: 1, 2, 3
        }

        // Example 5: Check for empty collections
        List<int> emptyList = new List<int>();
        if (emptyList.Count > 0)
        {
            Console.WriteLine(emptyList[0]);
        }
        else
        {
            Console.WriteLine("Collection is empty"); // Output: Collection is empty
        }
    }
}

---