Add explanatory comments to sample 3

src/sample_3.cpp

-#include <iostream>
 #include "sample_3.h"
+#include <iostream>
 
+// This function is passed a copy of the original house (no &)
+// Then the copy is painted black but the original still has its original color
+void city::copy_repaint(city::House torepaint) { torepaint.color = black; }
 
-void city::copy_repaint(city::House torepaint) {
-	torepaint.color = black;
-}
-
+// This function is passed a reference to the original house (&)
+// Then this house is painted black
 void city::copy_free_repaint(city::House& torepaint) {
     torepaint.color = black;
 }
@@ -13,8 +14,7 @@ void city::copy_free_repaint(city::House &torepaint) {
 void city::describe_house(city::House& house) {
     std::cout << "The resident " << house.owner;
     std::cout << " is currently living in their ";
-	switch (house.color)
-	{
+    switch (house.color) {
     case red:
         std::cout << "red";
         break;
@@ -38,10 +38,10 @@ void city::describe_house(city::House &house) {
 }
 
 int main(int argc, char** argv) {
-	using std::string;
-	using std::cout;
     using std::cin;
+    using std::cout;
     using std::endl;
+    using std::string;
     using namespace city;
 
     // Declare a variable to hold the name of the user
@@ -58,12 +58,14 @@ int main(int argc, char** argv) {
         // Check if the name has at least 3 characters
         if (owner.length() < 3) {
             // Print out hint
-			cout << "Your name is suspiciously short. Please enter at least 3 characters" << endl;
+            cout << "Your name is suspiciously short. Please enter at least 3 "
+                    "characters"
+                 << endl;
             // Skip to next run of loop
             continue;
-		}
-		else {
-			// Write out a mix of a static string and the string previously read in
+        } else {
+            // Write out a mix of a static string and the string previously read
+            // in
             cout << "So your name is " << owner << "." << endl;
 
             // Let us break free of this infinite loop
@@ -71,7 +73,6 @@ int main(int argc, char** argv) {
         }
     }
 
-
     // Let's ask the user for a color of the house
     cout << "Which color should your house have? (r|g|b|w)" << endl;
 
@@ -107,12 +108,14 @@ int main(int argc, char** argv) {
 
         // Deal with an unknown color
         if (unknown_color) {
-			cout << "The color you chose was not known. Please choose one out of r,g,b,w" << endl;
+            cout << "The color you chose was not known. Please choose one out "
+                    "of r,g,b,w"
+                 << endl;
             // Retry
             continue;
-		}
-		else {
-			cout << "The color you chose was " << color << ". Your house will be painted in this color." << endl;
+        } else {
+            cout << "The color you chose was " << color
+                 << ". Your house will be painted in this color." << endl;
             // End loop
             break;
         }
@@ -129,18 +132,19 @@ int main(int argc, char** argv) {
         cin >> house_number;
 
         if (house_number <= 0) {
-			cout << "Oh no! Your favorite house number should certainly be positive. Please consider this again." << endl;
+            cout << "Oh no! Your favorite house number should certainly be "
+                    "positive. Please consider this again."
+                 << endl;
             // Retry
             continue;
-		}
-		else {
-			cout << "Oh, so your house will have the number " << house_number << " just for you." << endl;
+        } else {
+            cout << "Oh, so your house will have the number " << house_number
+                 << " just for you." << endl;
             // Stop the trying loop
             break;
         }
     }
 
-
     // Declare a house of custom type and assign its member fields.
     House designed_house;
     designed_house.color = houseColor;
@@ -150,17 +154,16 @@ int main(int argc, char** argv) {
     std::cout << "Let us summarize your registration:" << endl;
     describe_house(designed_house);
 
-	std::cout << "Let us summarize your registration:" << endl;
-	describe_house(designed_house);
-
     std::cout << "We will now try to repaint your house black:" << endl;
+    // Demonstrate that passing the copy of a house will not change the original
     copy_repaint(designed_house);
     describe_house(designed_house);
 
     std::cout << "Let us try it again a little differently:" << endl;
+    // Demonstrate that passing a reference to the original will cause its color
+    // to change
     copy_free_repaint(designed_house);
     describe_house(designed_house);
 
-
     return 0;
 }