added listing tag to blocks

Author: habibasorour

source/ch4_conditionals.ptx

@@ -264,19 +264,21 @@ 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 xml:id="python-square-input" interactive="activecode" language="python">
+        <listing xml:id="python-square-input">
+        <program interactive="activecode" language="python">
             <code>
             number = int(input("Please enter a whole number: "))
             squared = number ** 2
             print("Your number squared is " + str(squared))            
             </code>
         </program>
+        </listing>
 
         <p>
             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 xml:id="java-square-input" interactive="activecode" language="java">
+        <listing xml:id="java-square-input">
+        <program interactive="activecode" language="java">
             <code>
             import java.util.Scanner;
 
@@ -293,12 +295,13 @@ The <c>switch</c> statement is not used very often, and we recommend you do not
             }
             </code>
         </program>
+        </listing>
 
         <p>
             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 xml:id="python-square-input-exception" interactive="activecode" language="python">
+        <listing xml:id="python-square-input-exception">
+        <program interactive="activecode" language="python">
             <code>
             while True:
                 try:
@@ -310,12 +313,13 @@ The <c>switch</c> statement is not used very often, and we recommend you do not
                     print("That was not a valid number. Please try again: ")   
             </code>
         </program>
+        </listing>
 
         <p>
             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 xml:id="java-square-input-exception" interactive="activecode" language="java">
+        <listing xml:id="java-square-input-exception">
+        <program interactive="activecode" language="java">
             <code>
             import java.util.Scanner;
             import java.util.InputMismatchException;
@@ -340,6 +344,7 @@ The <c>switch</c> statement is not used very often, and we recommend you do not
             }
             </code> <stdin> </stdin> <tests> </tests>
         </program>
+        </listing>
 
         <p>
             Firstly, let's talk about the extra import alongside the <c>Scanner</c> import. In Java, we need to import <c>InputMismatchException</c> because it's not automatically available like basic exceptions. This is different from Python where most exceptions are readily accessible. If you ran the previous Java codeblock without <c>try-catch</c> blocks and entered an erroneous input, you would have got an <c>InputMismatchException</c> exception despite not having imported this class. That being said, removing the explicit import of this library for the <c>try-catch</c> code block above will lead to compilation errors.