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Commit 3a3aa32a authored by Goik Martin's avatar Goik Martin
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while intro

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Doc/Sd1/statements.xml
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......@@ -153,7 +153,7 @@
</figure>
<section xml:id="sd1_sect_statements_if">
<title>The if statement</title>
<title>The if conditional statement</title>
<figure xml:id="sd1_fig_if">
<title><code>if</code> ... <code>else</code> for block selection</title>
......@@ -900,9 +900,13 @@ Decimal value 11 not yet implemented</screen>
}
}</programlisting>
</figure>
</section>
<section xml:id="sd1_sect_switch">
<title>The <code>switch</code> statement</title>
<figure xml:id="sd1_fig_switch">
<title>Better: The <code>switch</code> statement</title>
<title>Better: Using <code>switch</code></title>
<programlisting language="java">...
switch(number) {
......@@ -1293,6 +1297,118 @@ Midweek</screen>
</qandaset>
</section>
<section xml:id="sd1_sect_loops">
<title><code>while</code>, <code>do ... while</code> and <code>for</code> loops</title>
<figure xml:id="sd1_fig_loopWhy">
<title>Why loops?</title>
<glosslist>
<glossentry>
<glossterm>Objective</glossterm>
<glossdef>
<para>Execute the same code multiple times.</para>
</glossdef>
</glossentry>
<glossentry>
<glossterm>Solution</glossterm>
<glossdef>
<para>Copy / paste the code in question:</para>
<programlisting language="java">System.out.println("Do not copy!");
System.out.println("Do not copy!");
System.out.println("Do not copy!");
System.out.println("Do not copy!");</programlisting>
</glossdef>
</glossentry>
<glossentry>
<glossterm>Problem</glossterm>
<glossdef>
<para>Only works if number of repetitions is known at compile time.</para>
</glossdef>
</glossentry>
</glosslist>
</figure>
<figure xml:id="sd1_fig_loopBadParameterization">
<title>Hard to parameterize</title>
<para>Limited workaround for repetition count given at runtime:</para>
<programlisting language="java">int repetitions;
repetitions = 3; // value dynamically set
switch(repetitions) {
case 5: System.out.println("Do not copy!");
case 4: System.out.println("Do not copy!");
case 3: System.out.println("Do not copy!");
case 2: System.out.println("Do not copy!");
case 1: System.out.println("Do not copy!");
}</programlisting>
<para>Problem: Clumsy and limited (five lines of output max.)</para>
</figure>
<figure xml:id="sd1_fig_loopParamSolution">
<title>A <code>while</code> loop</title>
<programlisting language="java">int repetitions = 3; <co linkends="sd1_callout_whileLoop-1" xml:id="sd1_callout_whileLoop-1-co"/>
int loopCounter = 1; <co linkends="sd1_callout_whileLoop-2" xml:id="sd1_callout_whileLoop-2-co"/>
while (loopCounter &lt;= repetitions <co linkends="sd1_callout_whileLoop-3" xml:id="sd1_callout_whileLoop-3-co"/>) {
System.out.println("Do not copy!"); <co linkends="sd1_callout_whileLoop-4" xml:id="sd1_callout_whileLoop-4-co"/>
loopCounter++; <co linkends="sd1_callout_whileLoop-5" xml:id="sd1_callout_whileLoop-5-co"/>
}</programlisting>
<screen>Do not copy!
Do not copy!
Do not copy!</screen>
</figure>
<calloutlist>
<callout arearefs="sd1_callout_whileLoop-1-co" xml:id="sd1_callout_whileLoop-1">
<para>Will be repeated this number of times</para>
</callout>
<callout arearefs="sd1_callout_whileLoop-2-co" xml:id="sd1_callout_whileLoop-2">
<para>Helper variable keeping track of repetitions</para>
</callout>
<callout arearefs="sd1_callout_whileLoop-3-co" xml:id="sd1_callout_whileLoop-3">
<para>Condition to be checked before each new execution.</para>
</callout>
<callout arearefs="sd1_callout_whileLoop-4-co" xml:id="sd1_callout_whileLoop-4">
<para>Statement(s) to be repeated.</para>
</callout>
<callout arearefs="sd1_callout_whileLoop-5-co" xml:id="sd1_callout_whileLoop-5">
<para>Increment helper variable each iteration.</para>
</callout>
</calloutlist>
<figure xml:id="sd1_fig_loopParamSolutionSyntaxSugar">
<title>Combining increment and termination condition</title>
<programlisting language="java">int repetitions = 3;
int loopCounter = 1;
while (loopCounter++ &lt;= repetitions) {
System.out.println("Do not copy!");
}</programlisting>
<screen>Do not copy!
Do not copy!
Do not copy!</screen>
</figure>
</section>
<section xml:id="ex">
<title>Exercises</title>
......@@ -1467,7 +1583,7 @@ Midweek</screen>
<qandadiv>
<qandaentry>
<question>
<para>Producing the following ASCII art for configurable Xmas tree sizes is a bit more challenging :</para>
<para>Producing the following ASCII art for configurable Xmas tree sizes is more challenging :</para>
<screen> \ /
--&gt;*&lt;--
......@@ -1529,7 +1645,7 @@ Midweek</screen>
System.out.println("--&gt;*&lt;--"); // "--&gt;*&lt;--" string.
for (int x = 0; x &lt; numberOfRowGroups + 1; x++) { // The tree's lower top "/ \".
System.out.print(' '); // We need numberOfRows+1
System.out.print(' '); // We need again numberOfRows+1
} // preceding spaces.
System.out.println("/_\\");
......@@ -1575,7 +1691,7 @@ Midweek</screen>
<para>So far we have not yet introduced methods. In anticipation of upcoming lessons we provide an alternate solution by introducing a method <methodname>printIndented(...)</methodname> which prints a string being indented by a given number of whitespace characters. The System.out.format(...) method will be explained in <xref linkend="sw1SectSquareNumbersFormatted"/>.</para>
<para>This effectively makes our code more readable:</para>
<para>This enhances our code's readability:</para>
<programlisting language="java">public class XmasTree {
......@@ -1639,8 +1755,7 @@ Midweek</screen>
//
printIndent (numberOfRowGroups, "[___]"); // Indenting the bottom trunk ...
}
}
</programlisting>
}</programlisting>
</answer>
</qandaentry>
</qandadiv>
......
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