Multidimensional arrays

Learn multidimensional arrays as matrices with int[,].

Multidimensional arrays

For row-and-column data you use a multidimensional array. The most common type is int[,], which represents a two-dimensional matrix: int[,] m = { { 1, 2 }, { 3, 4 } };.

Access uses two indices: m[0, 1] gives the first row's second column. m.GetLength(0) returns the row count and m.GetLength(1) the column count. Nested for loops walk every cell.

Walking a matrix with nested for

To walk every cell of a matrix you use two nested for loops. The outer loop walks rows, the inner loop walks columns: for (int i = 0; i < m.GetLength(0); i++) for (int j = 0; j < m.GetLength(1); j++) ... m[i, j] ....

This pattern suits walking student grades in a class or a chess board. The inner loop restarts on each row; so each (i, j) pair is visited exactly once.

Exercise Declare a matrix and print a cell

Declare a matrix m with the value { { 1, 2, 3 }, { 4, 5, 6 } } (two rows, three columns). Then print m[1, 2] with Console.WriteLine. The output should be 6.

Show example solution

Write int[,] m = { { 1, 2, 3 }, { 4, 5, 6 } }; and print it with Console.WriteLine(m[1, 2]);
Example solution:
using System;

class Program
{
    static void Main()
    {
        int[,] m = { { 1, 2, 3 }, { 4, 5, 6 } };
        Console.WriteLine(m[1, 2]);
    }
}

Test yourself

How many elements does int[,] m = new int[2, 3]; have?
```
int[,] m = new int[2, 3];
Console.WriteLine(m.Length);
```
- 6
- 5
- 3
- 2
Show answer

6 — Correct. 2 rows × 3 columns = 6 cells.
Match each matrix part to its meaning

int[,]

Two-dimensional array
GetLength(0)

Row count
GetLength(1)

Column count
m[1, 2]

Specific cell

Write the matrix cell index

int[,] m = new int[2, 3];
int v = m[____, 2];

Show answer

int[,] m = new int[2, 3];
int v = m[1, 2];

Next lesson: Jagged arrays

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