Multi-parameter indexers in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Multi-parameter indexers

Create object with multi-parameter indexer

↓

Call indexer with 2 parameters

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Indexer get or set method runs

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Access or modify internal data

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Return or store value

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Use value in main code

This flow shows how a multi-parameter indexer is called with two parameters, accesses internal data, and returns or sets a value.

Execution Sample

C Sharp (C#)

class Matrix {
  private int[,] data = new int[2,2];
  public int this[int row, int col] {
    get => data[row, col];
    set => data[row, col] = value;
  }
}

var m = new Matrix();
m[0,1] = 5;
var x = m[0,1];

This code creates a 2x2 matrix with a multi-parameter indexer to get and set values by row and column.

Execution Table

Step	Action	Parameters	Internal Data Access	Result/Output
1	Create Matrix object	-	data initialized as [[0,0],[0,0]]	-
2	Set value via indexer	row=0, col=1, value=5	data[0,1] set to 5	-
3	Get value via indexer	row=0, col=1	data[0,1] accessed, value=5	5
4	Use value in main code	-	-	x = 5
5	End	-	-	Program ends

💡 All steps complete; program ends after value retrieval.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
data	[[0,0],[0,0]]	[[0,5],[0,0]]	[[0,5],[0,0]]	[[0,5],[0,0]]
x	undefined	undefined	5	5

Key Moments - 2 Insights

Why do we use two parameters inside the indexer brackets?

Because the indexer is defined to take two parameters (row and column), so both are needed to access the correct element in the 2D array, as shown in execution_table step 2 and 3.

What happens if we try to get a value before setting it?

The value returned would be the default for int, which is 0, because the array is initialized with zeros. This is implied in step 1 where data starts with zeros.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of data after step 2?

A [[0,0],[5,0]]

B [[5,0],[0,0]]

C [[0,5],[0,0]]

D [[0,0],[0,5]]

💡 Hint

Check the 'Internal Data Access' column in step 2 of execution_table.

At which step is the value 5 assigned to variable x?

A Step 2

B Step 4

C Step 3

D Step 1

💡 Hint

Look at the 'Result/Output' column for step 4 in execution_table.

If we changed m[0,1] = 5 to m[1,0] = 7, what would data look like after step 2?

A [[0,0],[7,0]]

B [[0,5],[0,0]]

C [[7,0],[0,0]]

D [[0,0],[0,7]]

💡 Hint

Remember data is a 2D array indexed by [row, col], see variable_tracker for data layout.

Concept Snapshot

Multi-parameter indexers let you use multiple values inside [] to get or set data.
Syntax: public type this[type1 i, type2 j] { get; set; }
Useful for 2D data like matrices.
Access like obj[i,j].
Behind the scenes, get or set runs with those parameters.

Full Transcript

This example shows how a C# class can use a multi-parameter indexer to access elements in a 2D array. The indexer takes two parameters, row and column, to get or set values inside the internal array. The execution table traces creating the object, setting a value at position [0,1], then getting that value back. The variable tracker shows how the internal data array changes after setting the value, and how the variable x receives the retrieved value. Key moments clarify why two parameters are needed and what happens if you get a value before setting it. The visual quiz tests understanding of data changes and variable assignments during execution. The concept snapshot summarizes the syntax and purpose of multi-parameter indexers in simple terms.