5 key learning points in Lab 5

1. Write a class in C++ (destructor, overloading)
2. Inheritance in C++ (overridding, pure method)
3. Polymophism in C++ (virtual, pointers and references)
4. Putting everything together into an array of objects (again!)
5. Separting into header (.h) and implementation (.cpp) files

1. Write a class in C++

							~Animal() {
								cout << "destructing Animal object "<< _name << endl ;
							}
						

Q: Why are destructors needed in C++?
C++ does not have in-built garbage collection (there are external ones), so some manual memory management is needed. But there are also smart pointers now.

Q: Why doesn't C++ use garbage collectors? (GC works well in Java!)
It's complicated, but tl;dr - C/C++ is a little too low level for GC to work well (+ remember that C/C++ is also meant to work on extremely low-resource settings - even a simple GC will create too much overhead)

2. Inheritance in C++

							class Shape {
								public :
								Shape() { }
								virtual void area() = 0 ;
								// virtual void area() { cout << "undefined" << endl ;}
								void name() { cout << " a shape" << endl ; }
							};

							class Rectangle : public Shape {
								...
								public :
								Rectangle(int x, int y) : _length(x) , _height(y) { }
								void area() { cout << "area is " << _length * _height << endl ; }
							}
						

// Make sure you watch out for the function signatures when you define the sub-classes - they should be the same! (i.e. if there is a `const` in your method in the superclass, it should be in your sub-class too)

3. Polymophism in C++

							int main() {
								Rectangle rect(10,20);
								Shape *shapePtr = &rect ;
								Shape &shapeRef = rect ;
								Shape shapeVal = rect ;
								
								shapePtr->area() ;
								shapeRef.area() ;
								shapeVal.area() ;
							}
						

Without virtual, all 3 lines will print the same thing
(i.e. "undefined")

More about pointers and references here (section 2.4).

4. Array of Objects (build a zoo)

• Having an array of 3 objects (🐶,😸,🦁) is fine, if you want to have more that's fine too as long as you don't run into any errors
• You need to initialize your arrays (e.g. 0 or Mammal object) so that you don't run into issues (like uninitialized values) when iterating through the loop when the Zoo is not full 🙈
• Sending an animal to the zoo will then mean that you're replacing the value of the existing (null) value / object in the array
• Remember to free the animals at the end (i.e. delete the objects and free up memory)

5. Header and Implementation

More scaffolds

• Not in lab and Visual Studio takes up too much space? Eclipse works, CodeBlocks too or even VSCode (weird errors though)
• Recap about the difference between compiling, linking and building
• You might need to have #include guards. Here's how it works.
• Destructors can be virtual too, some IDEs might warn but it's fine
• You'll face issues printing the value stored in the enum - here's one way to solve it and here are more ways to solve it. But you can fix it with switch statements too.