Adding some exercises on 2d arrays.

Author: Clément

source/code/snippets/2darrays.cs

@@ -0,0 +1,58 @@
+using System;
+
+class Program
+{
+    static void Main()
+    {
+        // Example array1
+        int[,] matrix =
+        {
+      { 1, 2, 3 },
+      { 4, 5, 6 },
+      { 7, 8, 9 },
+      { 10, 11, 12 },
+    };
+        // End of example array1
+        Display(matrix);
+        Rotate(ref matrix);
+        Display(matrix);
+    }
+
+    // Method to display 2-d arrays
+    static void Display(int[,] matP)
+    {
+        for (int row = 0; row < matP.GetLength(0); row++)
+        {
+            for (int col = 0; col < matP.GetLength(1); col++)
+            {
+                Console.Write(
+                  String.Format("|{0,4} ", matP[row, col])
+                );
+            }
+            Console.WriteLine(" |");
+        }
+    }
+
+    // End of method to display 2-d arrays
+
+    // Method to rotate an array 90° clockwise
+    static void Rotate(ref int[,] matP)
+    {
+        int[,] tmp = new int[
+          matP.GetLength(1),
+          matP.GetLength(0)
+        ];
+        for (int row = 0; row < tmp.GetLength(0); row++)
+        {
+            for (int col = 0; col < tmp.GetLength(1); col++)
+            {
+                tmp[row, col] = matP[
+                  tmp.GetLength(1) - col - 1,
+                  row
+                ];
+            }
+        }
+        matP = tmp;
+    }
+    // End of method to rotate an array 90° clockwise
+}

source/solutions/collections/2darrays.md

@@ -65,7 +65,7 @@ tags:
     | 40  | 50  | 60  | 
     | 70  | 80  | 90  | 
 
-        <details>
+    <details>
     <summary>Solution</summary>
 
     ```
@@ -112,6 +112,14 @@ tags:
     By using the `Length` field: `temp.Length` is the number of elements in the `temp` array.
     We can also compute the product of `temp.GetLength(0)` and `temp.GetLength(1)`.
     </details>
+    
+#. Write a `Display` static method that takes as an argument a 2-dimensional array and displays it at the screen.
+
+    <details>
+    <summary>Solution</summary>```
+    !include`snippetStart="// Method to display 2-d arrays", snippetEnd="// End of method to display 2-d arrays"`  code/snippets/2darrays.cs
+    ```
+    </details>
 
 #. Write a program that display "Every row contains its own index" if the 2-dimensional rectangular array of `int` `matrix` is such that its first row contains the value 0, its second row contains the value 1, etc.
 
@@ -172,6 +180,26 @@ tags:
     ```
     </details>
 
+#. Write a program that "rotate" a 2-dimensional array 90° clockwise. For example, the array 
+
+    ```
+    !include`snippetStart="// Example array1", snippetEnd="// End of example array1"`  code/snippets/2darrays.cs
+    ```
+    
+    would become
+    
+    ```text
+    |  10 |   7 |   4 |   1  |
+    |  11 |   8 |   5 |   2  |
+    |  12 |   9 |   6 |   3  |
+    ```
+
+    <details>
+    <summary>Solution</summary>```
+    !include`snippetStart="// Method to rotate an array 90° clockwise", snippetEnd="// End of method to rotate an array 90° clockwise"`  code/snippets/2darrays.cs
+    ```
+    </details>
+
 ## Problem: Toward a Crossword Puzzle Solver
 
 The goal of this problem is to work toward the creation of a program that solve crossword puzzles.
@@ -191,9 +219,9 @@ Test your program thoroughly, possibly bundling it in a `static` class to ease t
 <details>
 <summary>Solution</summary>
 A possible implementation, as a static class, is as follows:
-
 ```{download="./code/projects/CrossWord.zip"}
-!include code/projects/CrossWord/CrossWord/CrossWord.cs
-```</details>
+!include code/projects/CrossWord/CrossWord/Crossword.cs
+```
 </details>
 
+