From 057d3a31cb08c0325951f3f9fe0f2b04c306dd21 Mon Sep 17 00:00:00 2001
From: Martin Goik <goik@hdm-stuttgart.de>
Date: Wed, 7 Feb 2024 07:11:33 +0100
Subject: [PATCH] Better code error explanation

---
 Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml | 84 +++++++++++++++++-----
 1 file changed, 65 insertions(+), 19 deletions(-)

diff --git a/Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml b/Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml
index 5b8cfbf8a..247e9a9c9 100644
--- a/Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml
+++ b/Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml
@@ -107,7 +107,15 @@
           <answer>
             <para>There are errors:</para>
 
-            <programlisting language="java">/**
+            <informaltable border="1">
+              <tr>
+                <th>Erroneous code</th>
+
+                <th>Correct code</th>
+              </tr>
+
+              <tr>
+                <td valign="top"><programlisting language="java">/**
  * Summing up an int array's values
  *
  * @param values An array of int values
@@ -116,35 +124,54 @@
 public static int sum(int[] values) {
 
    int sum; <co linkends="sd1_exam_2023_winter_sumErrors-1"
-                xml:id="sd1_exam_2023_winter_sumErrors-1-co"/>
+                      xml:id="sd1_exam_2023_winter_sumErrors-1-co"/>
 
    for (<co linkends="sd1_exam_2023_winter_sumErrors-2"
-                xml:id="sd1_exam_2023_winter_sumErrors-2-co"/> i = 0; i &lt;=<co
-                linkends="sd1_exam_2023_winter_sumErrors-3"
-                xml:id="sd1_exam_2023_winter_sumErrors-3-co"/> values.length; i++) {
+                      xml:id="sd1_exam_2023_winter_sumErrors-2-co"/> i = 0; i &lt;=<co
+                      linkends="sd1_exam_2023_winter_sumErrors-3"
+                      xml:id="sd1_exam_2023_winter_sumErrors-3-co"/> values.length; i++) {
+        sum += values[i];
+   }
+   return sum;
+}</programlisting></td>
+
+                <td valign="top"><programlisting language="java">/**
+ * Summing up an int array's values
+ *
+ * @param values An array of int values
+ * @return The sum of all array values
+ */
+public static int sum(int[] values) {
+
+   int sum = 0;
+
+   for (int i = 0; i &lt; values.length; i++) {
         sum += values[i];
    }
    return sum;
-}</programlisting>
+}</programlisting></td>
+              </tr>
+            </informaltable>
 
             <calloutlist>
               <callout arearefs="sd1_exam_2023_winter_sumErrors-1-co"
                        xml:id="sd1_exam_2023_winter_sumErrors-1">
-                <para>Missing initialization <code language="java">int sum =
+                <para>Missing initialization <code language="java">sum =
                 0</code>.</para>
               </callout>
 
               <callout arearefs="sd1_exam_2023_winter_sumErrors-2-co"
                        xml:id="sd1_exam_2023_winter_sumErrors-2">
-                <para>Missing type i.e. <code language="java">int i =
-                0</code>;</para>
+                <para>Missing type i.e. <code language="java">int
+                i</code>.</para>
               </callout>
 
               <callout arearefs="sd1_exam_2023_winter_sumErrors-3-co"
                        xml:id="sd1_exam_2023_winter_sumErrors-3">
                 <para>Off by one error: Last array index being <code
                 language="java">values.length - 1</code> requires <code
-                language="java">i &lt; values.length</code>.</para>
+                language="java">i &lt; values.length</code> avoiding an
+                <classname>ArrayIndexOutOfBoundsException</classname>.</para>
               </callout>
             </calloutlist>
           </answer>
@@ -174,33 +201,52 @@ public static int sum(int[] values) {
           </question>
 
           <answer>
-            <para>Every expression of type byte is bounded by <code
-            language="java">Byte.MAX_VALUE</code>. The expression <code
-            language="java">b &lt;= Byte.MAX_VALUE</code> is thus always
+            <para>Every variable of type byte is bounded by <code
+            language="java">Byte.MAX_VALUE</code>. The boolean expression
+            <code language="java">b &lt;= Byte.MAX_VALUE</code> is thus always
             true.</para>
 
-            <para>A closer look on the operator ++ acting on a byte variable
-            reveals a cycle passing between <code
-            language="java">Byte.MIN_VALUE</code> and <code
-            language="java">Byte.MAX_VALUE</code>:</para>
+            <para>An even closer look reveals <code language="java">b++</code>
+            oscillating between its lower <code
+            language="java">Byte.MIN_VALUE</code> and upper <code
+            language="java">Byte.MAX_VALUE</code> bound:</para>
 
             <informaltable border="1">
+              <colgroup width="36%"/>
+
+              <colgroup width="12%"/>
+
+              <colgroup width="52%"/>
+
               <tr>
                 <th>Code</th>
 
                 <th>Output</th>
+
+                <th>Explanation</th>
               </tr>
 
               <tr>
                 <td valign="top"><programlisting language="java">byte b = Byte.MAX_VALUE - 1;
 System.out.println(b++);
 System.out.println(b++);
+System.out.println(b++);
+...
 System.out.println(b++);</programlisting></td>
 
                 <td valign="top"><screen> 126
- 127
+ <emphasis role="red">127</emphasis>
 -128
--127</screen></td>
+-127
+ ...
+ <emphasis role="red">127</emphasis></screen></td>
+
+                <td valign="top"><screen>
+Byte.MAX_VALUE
+Byte.MIN_VALUE
+
+
+Byte.MAX_VALUE</screen></td>
               </tr>
             </informaltable>
 
-- 
GitLab