1. Two-Dimension Arrays
Computer Programming 2

2. Objective/Essential Standard
Essential Standard 3.00 Apply Advanced Properties of Arrays
Essential Indicator 3.01 Apply procedures to construct two-dimensional arrays. (6%)

3. Two-Dimensional Arrays
Two-Dimensional Array = Rectangular Array
A two-dimensional array contains rows and columns.
This type of array requires two indices, one for the row and one for the column

4. Two-Dimensional Arrays
Declaring a two-dimensional array dataType [ , ] name = new dataType [r, c];
where r = the number of rows and c = the number of columns.
Example int [ , ] intArray = new int[3, 3];
This would declare a 3 by 3 array. 1 2 1 2

5. Declaring & Initializing a Two-Dimensional Array
Example 1
Declare with an initializer list
int[,] numbers = new int[3, 2] { {1, 2}, {3, 4}, {5, 6} }; string[,] friends = new string[2, 2] { {"Mike","Anna"}, {"Mary",“John"} };
Example 2
You can omit the size of the array with an initializer list.
int[,] numbers = new int[ , ] { {1, 2}, {3, 4}, {5, 6} }; string[,] friends = new string[ , ] { {"Mike","Anna"}, {"Mary",“John"} };
Example 3
You can omit the size of the array and the new operator if you provide the initializer list.
int[,] numbers = int[ , ] { {1, 2}, {3, 4}, {5, 6} }; string[,] friends = string[ , ] { {"Mike","Anna"}, {"Mary",“John"} };

6. Adding Values Individually
You can add values into your array as follows. intArray[r, c] = value;
Example: intArray[1, 1] = 3; 1 2 3 1 2

7. Accessing Values in a Two-Dimensional Array
Nested For Loops give you more control.
Use GetLength() to return how many elements are in that “Dimension”.
O is Dimension 1 (rows)
1 is Dimension 2 (columns)
int[,] intArr= new int[ , ] {{9, 99}, {3, 33}, {5, 55}}; for (int r = 0; r < intArr.GetLength(0); r++) { for (int c = 0; c < intArr.GetLength(1); c++) { Statements; } }

8. Creating a Grid
In XNA you can create a grid of rectangles that you can use to mimic a gameboard.
Declaring the two-dimensional array of rectangles.
Rectangle [ , ] grid = new Rectangle[2, 2];

9. Load the Rectangles into the Grid
for (int i = 0; i < grid.GetLength(0); i++) { for (int j = 0; j < grid.GetLength(1); j++) grid[i, j] = new Rectangle(x, y, 50, 50); x += 50; //change the x location } y += 50; //move y location down x = 0; //reset the x

10. Nested For Loops The Nested For Loop can be used in:
The Initialize method to load your images
picArray[i, j] = Content.Load<Texture2D>(“image");
The Draw method to “draw” your images
SpriteBatch.Draw(picArray[i,j], grid[i,j], Color.White);

11. Check Your Understanding
Declare an array called nums that will hold 5 integers.
int[] nums = new int[5];
What are the index numbers of the num array?
0, 1, 2, 3, 4
Given the nums array just declared, how would you write the for loop to traverse it?
for (int i = 0; i < 5; i++)

12. Check Your Understanding
Declare the table array represented below.
int [,] table = new int {{8,7}, {6,5}, {4,3}};
Given the table array, what would be the result of the following statement? Table[3,2] = 9;
Code won’t compiler because the index is out of bounds. 8 7 6 5 4 3

13. Check Your Understanding
Write the for loop to iterate through the 2D array called matrix.
for (int i = 0; i < matrix.GetLength(0); i++) for (int j = 0; j < matrix.GetLength(1); j++)
What code would be inside the above nested loop if you wanted to create a running total?
sum += matrix[i, j];

14. More Information
For more information about the Array class: