From 151c46fddded7b825bbcc93ef6a13eddd5dac1ba Mon Sep 17 00:00:00 2001
From: Martin Goik <goik@hdm-stuttgart.de>
Date: Tue, 6 Feb 2024 21:43:54 +0100
Subject: [PATCH] Enhancing endless loop solution
---
Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml | 112 +++++++++++----------
1 file changed, 61 insertions(+), 51 deletions(-)
diff --git a/Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml b/Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml
index 1e6cbf19b..5b8cfbf8a 100644
--- a/Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml
+++ b/Doc/Sd1/Appendix/Exam/2023/Winter/exam.xml
@@ -107,39 +107,46 @@
<answer>
<para>There are errors:</para>
- <glosslist>
- <glossentry>
- <glossterm>Line 9</glossterm>
-
- <glossdef>
- <para>The variable <code language="java">sum</code> lacks
- initialization e.g. <code language="java">int sum =
- 0</code>.</para>
- </glossdef>
- </glossentry>
-
- <glossentry>
- <glossterm>Line 16</glossterm>
-
- <glossdef>
- <para>There are two errors here:</para>
-
- <itemizedlist>
- <listitem>
- <para>Variable i has not been declared: <code
- language="java">for(int i = 0; ...</code></para>
- </listitem>
-
- <listitem>
- <para>The loop's upper limit is being breached: <code
- language="java">i < values.length</code> rather than
- <code language="java">i <= values.length</code> is
- being required.</para>
- </listitem>
- </itemizedlist>
- </glossdef>
- </glossentry>
- </glosslist>
+ <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; <co linkends="sd1_exam_2023_winter_sumErrors-1"
+ 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 <=<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>
+
+ <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 =
+ 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>
+ </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 < values.length</code>.</para>
+ </callout>
+ </calloutlist>
</answer>
</qandaentry>
</qandadiv>
@@ -167,9 +174,15 @@
</question>
<answer>
- <para>The operator ++ acting on a byte variable will cycle between
- <code language="java">Byte.MIN_VALUE</code> and <code
- language="java">Byte.MAX_VALUE</code>. Consider:</para>
+ <para>Every expression of type byte is bounded by <code
+ language="java">Byte.MAX_VALUE</code>. The expression <code
+ language="java">b <= 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>
<informaltable border="1">
<tr>
@@ -179,26 +192,23 @@
</tr>
<tr>
- <td valign="top"><programlisting language="java">byte b = Byte.MAX_VALUE;
-System.out.println(b);
-b++;
-System.out.println(b);</programlisting></td>
-
- <td valign="top"><screen>127
--128</screen></td>
+ <td valign="top"><programlisting language="java">byte b = Byte.MAX_VALUE - 1;
+System.out.println(b++);
+System.out.println(b++);
+System.out.println(b++);</programlisting></td>
+
+ <td valign="top"><screen> 126
+ 127
+-128
+-127</screen></td>
</tr>
</informaltable>
- <para>Before breaching the loop's upper limit <code
+ <para>Instead of breaching the loop's upper limit <code
language="java">Byte.MAX_VALUE</code> our variable <code
- language="java">b will thus transition</code> from Byte.MAX_VALUE
- to <code language="java">Byte.MIN_VALUE</code>. The loop will thus
+ language="java">b will transition</code> from Byte.MAX_VALUE to
+ <code language="java">Byte.MIN_VALUE</code>. The loop will thus
continue forever.</para>
-
- <para>Shorter explanation: The expression <code language="java">b
- <= Byte.MAX_VALUE</code> is always true due to <code
- language="java">Byte.MAX_VALUE</code>'s definition with respect to
- any value of type <code>byte</code>.</para>
</answer>
</qandaentry>
</qandadiv>
--
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