From ea1be0ef34d0c9e82d688b614f52db971a39b6b8 Mon Sep 17 00:00:00 2001
From: Martin Goik <goik@hdm-stuttgart.de>
Date: Sun, 13 Sep 2015 19:34:45 +0200
Subject: [PATCH] Simple interest exercise
---
Doc/Sd1/languageFundamentals.xml | 109 ++++++++++++++++++++++++++++++-
1 file changed, 107 insertions(+), 2 deletions(-)
diff --git a/Doc/Sd1/languageFundamentals.xml b/Doc/Sd1/languageFundamentals.xml
index 62138dcb1..d31450d6a 100644
--- a/Doc/Sd1/languageFundamentals.xml
+++ b/Doc/Sd1/languageFundamentals.xml
@@ -655,7 +655,7 @@ System.out.println("Maximum short value:" + maximum);
<title>Simple expressions</title>
<qandaset defaultlabel="qanda" xml:id="sw1QandaSquareArea">
- <title>Calculating the area of a square</title>
+ <title>Calculating square's area</title>
<qandadiv>
<qandaentry>
@@ -749,6 +749,111 @@ System.out.println("Maximum short value:" + maximum);
</qandadiv>
</qandaset>
+ <section xml:id="sd1SectInterestSimple">
+ <title>Interest calculation</title>
+
+ <qandaset defaultlabel="qanda" xml:id="sd1QandaInterestSimple">
+ <qandadiv>
+ <qandaentry>
+ <question>
+ <para>We want to calculate the compounded interest starting from
+ an initial capital, a given annual interest rate and a duration
+ of three years. Consider the following code fragment:</para>
+
+ <programlisting language="noneJava"> public static void main(String[] args) {
+
+ final double initialCapital = 223.12;
+ final double interestRate = 1.5;
+
+ System.out.println("Initial capital:" + initialCapital);
+ System.out.println("Annual interest rate:" + interestRate);
+
+ // TODO ...
+
+ System.out.println("Capital after three years:" + ...);
+ }</programlisting>
+
+ <para>The expected output is:</para>
+
+ <programlisting language="noneJava">Initial capital:223.12
+Annual interest rate:1.5
+Capital after three years:233.31175902999993</programlisting>
+
+ <tip>
+ <para>In case you are unsure read about calculating the
+ compounded interest.</para>
+ </tip>
+ </question>
+
+ <answer>
+ <para>We obtain the compounded interest by multiplying the
+ initial capital by <inlineequation>
+ <m:math display="inline">
+ <m:mrow>
+ <m:mn>1</m:mn>
+
+ <m:mo>+</m:mo>
+
+ <m:mrow>
+ <m:mi>r</m:mi>
+
+ <m:mo>/</m:mo>
+
+ <m:mn>100</m:mn>
+ </m:mrow>
+ </m:mrow>
+ </m:math>
+ </inlineequation> for each year where r represents the given
+ interest rate.</para>
+
+ <para>Since we have not yet introduced loops this multiplication
+ has to be repeated three times:</para>
+
+ <programlisting language="noneJava"> public static void main(String[] args) {
+
+ final double initialCapital = 223.12;
+ final double interestRate = 1.5;
+
+ System.out.println("Initial capital:" + initialCapital);
+ System.out.println("Annual interest rate:" + interestRate);
+
+ final double factor = 1. + interestRate/100.;
+ double capitalAtThreeYears = initialCapital;
+
+ capitalAtThreeYears *= factor; // Year 1
+ capitalAtThreeYears *= factor; // Year 2
+ capitalAtThreeYears *= factor; // Year 3
+
+ System.out.println("Capital after three years:" + capitalAtThreeYears);
+ }</programlisting>
+
+ <para>We might as well use a single arithmetic expression to
+ achieve the same result:</para>
+
+ <programlisting language="noneJava"> public static void main(String[] args) {
+
+ final double initialCapital = 223.12;
+ final double interestRate = 1.5;
+
+ System.out.println("Initial capital:" + initialCapital);
+ System.out.println("Annual interest rate:" + interestRate);
+
+ final double factor = 1. + interestRate/100.;
+ final double capitalAtThreeYears =
+ initialCapital * factor * factor * factor;
+
+ System.out.println("Capital after three years:" + capitalAtThreeYears);
+ }</programlisting>
+
+ <para>In <xref linkend="sd1InterestCalculator"/> we will present
+ a more elaborate solution based on loops and class
+ methods.</para>
+ </answer>
+ </qandaentry>
+ </qandadiv>
+ </qandaset>
+ </section>
+
<section xml:id="sd1ExpressionStrangeThings">
<title>Strange things happen</title>
@@ -772,7 +877,7 @@ System.out.println("New value=" + a);
New value=-128</programlisting>
<para>Explain this strange behaviour. Moreover you'll find the
- following code yields a compile time error:</para>
+ following code snippet yields a compile time error:</para>
<programlisting language="noneJava">byte a = 127;
System.out.println("value=" + a);
--
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