How to Resolve Error "CS0022: Wrong number of indices inside []; expected 'number'" in C#

The Compiler Error CS0022 is a dimensionality mismatch error. The message reads: "Wrong number of indices inside []; expected 'number'".

This error occurs when you attempt to access an element within an array (or a collection with an indexer) using the wrong number of coordinates. For example, trying to access a 2D grid using only one number, or trying to access a standard list using two numbers.

This guide explains the difference between standard arrays, multi-dimensional matrices, and jagged arrays to help you fix your indexing syntax.

Understanding Array Dimensions

In C#, square brackets [] are used to access data. The number of values you put inside the brackets depends on how the data structure was defined:

• 1D Array (int[]): Requires 1 index. Example: arr[0]
• 2D Array / Matrix (int[,]): Requires 2 indices. Example: arr[0, 1]
• Jagged Array (int[][]): Requires chained indices. Example: arr[0][1]

CS0022 happens when the definition and the usage do not match.

Scenario 1: The Matrix (Multi-dimensional Arrays)

A common mistake is treating a multi-dimensional array (defined with a comma [,]) as if it were a single-dimensional list.

Example of Mistake

You define a grid (e.g., a chessboard or spreadsheet), but try to access a "row" using a single index. Unlike C++, accessing just the row of a C# [,] array is not allowed via indexing; you must specify both coordinates to get a value.

public void ProcessGrid()
{
    // A 3x3 Matrix
    int[,] matrix = new int[3, 3] {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };

    // ⛔️ Error CS0022: Wrong number of indices inside []; expected 2
    // You cannot access a whole row like this in a Rectangular Array.
    var val = matrix[0]; 
}

Solution

You must provide both the Row and the Column index.

public void ProcessGrid()
{
    int[,] matrix = new int[3, 3];

    // ✅ Correct: Access row 0, column 1
    int val = matrix[0, 1]; 
}

Scenario 2: The Jagged Array Confusion

Jagged arrays are "arrays of arrays." They are defined with side-by-side brackets [][] rather than a comma [,]. A common error is trying to access them using the comma syntax specific to matrices.

Example of Mistake

Trying to use [x, y] syntax on a jagged array.

public void ProcessJagged()
{
    // A Jagged Array (An array containing 3 arrays)
    int[][] jagged = new int[3][];
    jagged[0] = new int[] { 1, 2 };

    // ⛔️ Error CS0022: Wrong number of indices inside []; expected 1
    // The variable 'jagged' is technically a 1D array (holding other arrays).
    // It expects 1 index to get the inner array. 
    // '[0, 1]' passes 2 indices, which is wrong for the outer array.
    int val = jagged[0, 1];
}

Solution

Use chained brackets. The first [0] selects the inner array, and the second [1] selects the element within that inner array.

public void ProcessJagged()
{
    int[][] jagged = new int[3][];
    jagged[0] = new int[] { 1, 2 };

    // ✅ Correct: "Get array at 0", then "Get item at 1 from that array"
    int val = jagged[0][1];
}

note

Memory Aid:

• If the declaration has a comma [,], the access needs a comma [x, y].
• If the declaration has separate brackets [][], the access needs separate brackets [x][y].

Scenario 3: Standard Arrays and Lists

Sometimes, this error is a simple typo where a user accidentally adds an extra comma inside the brackets of a standard 1D array or List.

Example of Mistake

using System.Collections.Generic;

public void ProcessList()
{
    List<string> names = new List<string> { "Alice", "Bob" };
    
    // ⛔️ Error CS0022: Wrong number of indices inside []; expected 1
    // Lists are 1-dimensional.
    string s = names[0, 1];
}

Solution

Remove the extra arguments.

public void ProcessList()
{
    List<string> names = new List<string> { "Alice", "Bob" };
    
    // ✅ Correct
    string s = names[0];
}

Conclusion

CS0022 is the compiler telling you that your coordinates don't match the map.

1. Check the declaration: Look at how the array was created (int[], int[,], or int[][]).
2. Match the syntax:
   • Type[] -> Use var[x]
   • Type[,] -> Use var[x, y]
   • Type[][] -> Use var[x][y]