Adding solution to first problem of exam #2.

Author: aubertc

source/code/projects/FileDisplayerSolution/FileDisplayerSolution/FileDisplayer.cs

@@ -1,6 +1,16 @@
 using System;
 using System.IO;
 
+/*
+ * Foreword: note that the project
+ * asks the method to display an error
+ * message if something goes wrong. A more
+ * principled approach would require the
+ * method to send an exception back to 
+ * the main routine, and to let it handle
+ * the error as it sees fit.
+ */
+
 static class FileDisplayer
 {
   public static void Display(string exP)

source/code/projects/RecursionDisplayH/RecursionDisplayH/Program.cs

@@ -0,0 +1,52 @@
+using System;
+using System.Collections.Generic;
+
+class Program
+{
+  static void Main(string[] args)
+  {
+    // DisplayH question
+    string DisplayH(int[] aP, int currentIndex)
+    {
+      string ret = "";
+      if (aP.Length == currentIndex + 1)
+        ret += " || " + aP[currentIndex].ToString();
+      else ret+= DisplayH(aP, currentIndex+1) + ", " + aP[currentIndex].ToString();
+      if (currentIndex == 0){ret += " ** "; }
+      return ret; 
+    }
+    string Display(int[] aP)
+    {
+      if (aP == null)
+        return "";
+      else
+        return DisplayH(aP, 0);
+    }
+    // Examples
+    int[] array0 = { 1, 2, 4};
+    int[] array1 = { 1, 2, 4, 10, 13, 17 };
+    int[] array2 = { 12, 98, 120, 15 };
+    int[] array3 =
+    {
+      1,
+      10,
+      12,
+      129,
+      190,
+      220,
+      230,
+      310,
+      320,
+      340,
+      400,
+      460,
+    };
+    Console.WriteLine("Example 0: " + Display(array0));
+    Console.WriteLine("Example 1: " + Display(array1));
+    Console.WriteLine("Example 2: " + Display(array2));
+    Console.WriteLine(
+      "Example 3: " + Display(array3)
+    );
+
+  }
+}

source/solutions/control/recursion.md

@@ -160,6 +160,17 @@ tags:
     Those are the first 6 digits of the [Fibonacci sequence](https://en.wikipedia.org/wiki/Fibonacci_sequence).
     </details>
 
+#. What would the following code display?
+
+    ```{download="./code/projects/RecursionDisplayH.zip"}
+    !include`snippetStart="// DisplayH question",snippetEnd="// Examples"` code/projects/RecursionDisplayH/RecursionDisplayH/Program.cs
+    ```
+    
+    <details>
+    <summary>Solution</summary>
+    It would display `|| 4, 2, 1 **`. You can download the solution above to execute the method and see for yourself. Note that the condition `currentIndex == 0`  adds the ` ** ` string *at the very end* of the string returned.
+    </details>
+    
 #. Rewrite the following `while` loop as a recursive method.
 
     ```{download="./code/projects/RecursionAndLoops.zip"}