add xml:ids to all programs in ch4

Author: pearcej

source/ch4_conditionals.ptx

@@ -16,7 +16,7 @@
             In Python the simple <c>if</c> statement is written as:
         </p>
 
-        <program interactive="activecode" language="python">
+        <program xml:id="python-simple-if" interactive="activecode" language="python">
             <code>
 score = 95
 if score &gt;= 90:
@@ -26,7 +26,7 @@ if score &gt;= 90:
         <p>
             In Java, this same pattern requires two changes: the condition must be in parentheses <c>()</c>, and the code block must be enclosed in curly braces <c>{}</c>.
         </p>
-        <program interactive="activecode" language="java">
+        <program xml:id="java-simple-if" interactive="activecode" language="java">
             <code>
             public class SimpleIfExample {
                 public static void main(String[] args) {
@@ -40,15 +40,15 @@ if score &gt;= 90:
         </program>
         <p>
             Once again you can see that in Java the curly braces define a block rather than indentation.
-            In Java the parenthesis around the condition are required because it is technically a function that evaluates to <c>True</c> or <c>False</c>.
+            In Java, the parentheses around the condition are required because it is technically a function that evaluates to <c>True</c> or <c>False</c>.
         </p>
     </section>
 
-    <section xml:id="if-else">
+    <section xml:id="use-the-if-else-statement">
         <title>Using the <c>if</c> - <c>else</c> Statement</title>
 
             <p>The Java equivalent follows the same syntactical rules as before.</p>
-        <program interactive="activecode" language="python">
+        <program xml:id="python-if-else" interactive="activecode" language="python">
             <code>
             age = 16
             if age &gt;= 18:
@@ -58,7 +58,7 @@ if score &gt;= 90:
             </code>
             </program>
 
-        <program language="java">
+        <program xml:id="java-if-else" language="java">
             <code>
         public class IfElseExample {
             public static void main(String[] args) {
@@ -84,7 +84,7 @@ if score &gt;= 90:
         </p>
 
 
-        <program interactive="activecode" language="python">
+        <program xml:id="python-if-nesting" interactive="activecode" language="python">
             <code>
 grade = int(input('enter a grade'))
 if grade &lt; 60:
@@ -101,11 +101,11 @@ else:
         </program>
 
         <p>
-In Java we have a couple of ways to write this.
+In Java, we have a couple of ways to write this.
         </p>
 
 
-        <program interactive="activecode" language="java">
+        <program xml:id="java-ifnesting" interactive="activecode" language="java">
             <code>
 public class ElseIf {
     public static void main(String args[]) {
@@ -133,12 +133,12 @@ public class ElseIf {
         </program>
 
         <p>
-We can get even closer to the <c>elif</c> statement by taking advantage of the Java rule that a single statement does not need to be enclosed in curly braces. Since the if is the only statement used in each else we can get away with the following.
+We can get even closer to the <c>elif</c> statement by taking advantage of the Java rule that a single statement does not need to be enclosed in curly braces. Since the <c>if</c> is the only statement used in each <c>else</c> block, we can get away with the following.
         </p>
 
 
 
-        <program interactive="activecode" language="java">
+        <program xml:id="java-if-else-no-nesting" interactive="activecode" language="java">
             <code>
 public class ElseIf {
     public static void main(String args[]) {
@@ -167,9 +167,9 @@ Java also supports a <c>switch</c> statement that acts something like the <c>eli
 
         <note>
             <p>
-                Depending on your knowledge and experience with Python you may already be familiar and questioning why we are not using the <c>match</c> statement in our Python examples. The answer is that this book currently runs its active code examples using Python 3.7, which does not support the <c>match</c> statement which was introduced in Python 3.10. Below is an example of the <c>match</c> statement similar to our grade method.
+                Depending on your knowledge and experience with Python you may be questioning why we are not using the <c>match</c> statement in our Python examples. The answer is that this book currently runs its active code examples using Python 3.7, which does not support the <c>match</c> statement which was introduced in Python 3.10. Below is an example of the <c>match</c> statement similar to our grade method.
             </p>
-                    <program language="python">
+                    <program xml:id="python-match" language="python">
             <title>Match Case Example</title>
             <code>
                 grade = 85
@@ -201,7 +201,7 @@ Java also supports a <c>switch</c> statement that acts something like the <c>eli
             Java 14 introduced <c>switch</c> <term>expressions</term>, enhancing functionality by allowing the <c>switch</c> to return values and eliminating <c>fall-through</c> via the <c>-&gt;</c> arrow syntax. These expressions can even use <c>yield</c> within code blocks for more complex evaluations. <term><c>yield</c></term> is used inside a switch expression’s block to produce the value of that expression, unlike <c>break</c> which simply exits a switch statement or loop. It’s important to note that traditional <c>switch</c> statements do not support <c>null</c> values and will throw a <c>NullPointerException</c> if evaluated with <c>null</c>. As the language evolves, newer versions of Java continue to extend <c>switch</c> capabilities with features like <c>pattern matching</c> and enhanced <c>type handling</c>, making it a more powerful and expressive tool for decision-making in Java programs.
         </p>
 
-        <program interactive="activecode" language="java">
+        <program xml:id="java-switch-up" interactive="activecode" language="java">
             <code>
             public class SwitchUp {
                 public static void main(String args[]) {
@@ -241,7 +241,7 @@ The <c>switch</c> statement is not used very often, and we recommend you do not
             In Python, if you want a program to continue running when an error has occurred, you can use <c>try-except</c> blocks to handle exceptions. If you wanted to write a program that asks the user to enter a whole number and then squares that number, you could use the following code to do so:
         </p>
 
-        <program interactive="activecode" language="python" xml:id="square-input-python">
+        <program xml:id="python-square-input" interactive="activecode" language="python">
             <code>
             number = int(input("Please enter a whole number: "))
             squared = number ** 2
@@ -253,7 +253,7 @@ The <c>switch</c> statement is not used very often, and we recommend you do not
             The Java code that would perform the same task is a little more complex and utilizes the <c>Scanner</c> class for input.
         </p>
 
-        <program interactive="activecode" language="java" xml:id="square-input-java">
+        <program xml:id="java-square-input" interactive="activecode" language="java">
             <code>
             import java.util.Scanner;
 
@@ -275,7 +275,7 @@ The <c>switch</c> statement is not used very often, and we recommend you do not
             This code works well, but will end with an exception if the user types anything other than a whole number (such as 12.5 or two). If we wanted to ensure the code will continue to run until the user enters the correct format, we could add <c>try-except</c> (Python) or <c>try-catch</c> (Java) blocks within a <c>while</c> loop that iterates until the user enter the correct code. Adding <c>try-except</c> blocks and a <c>while</c> loop to the Python code will look something like this:
         </p>
 
-        <program interactive="activecode" language="python" xml:id="square-input-exception-python">
+        <program xml:id="python-square-input-exception" interactive="activecode" language="python">
             <code>
             while True:
                 try:
@@ -292,7 +292,7 @@ The <c>switch</c> statement is not used very often, and we recommend you do not
             Now that we have Python code that will continuously prompt the user until they enter a whole number, let's look at Java code that accomplishes the same task. Like most other equivalent Java code blocks, this code has a lot of extra bits that are necessary to get working code. 
         </p>
 
-        <program interactive="activecode" language="java" xml:id="square-input-exception-java">
+        <program xml:id="java-square-input-exception" interactive="activecode" language="java">
             <code>
             import java.util.Scanner;
             import java.util.InputMismatchException;
@@ -439,7 +439,7 @@ of an assignment statement. The following table summarizes how this works:
 <p>
 Using this operator can make code shorter and more readable in cases where a simple conditional assignment is needed.
 </p>
-        <program interactive ="activecode" language ="java">
+        <program xml:id="java-ternary" interactive ="activecode" language ="java">
             <code>
                 class Main {
                         public static void main(String[] args) {