Week 5

Objects and Inheritance

• allows for one class to define itself in terms of another class
• "is-a" relationship
• e.g. a SortedIntArray is an IntArray

  class IntArray {
   public:
     IntArray();
     int length();
     int elementAt();
     int add();
   private:
     int l;
     int* a;
  }
  class SortedIntArray : public IntArray {
  }
  

• upcasts automatic and safe, downcasts can be unsafe

1. What objects would you make for a video game? How would they relate with each other?
2. Construct a derivation tree for the objects.

Polymorphism

1:	 class Simpson {
2:	 public:
3:	   virtual void greeting();
4:	   virtual void catchPhrase() = 0;
5:	   void parting();
6:	 }
7:	 
8:	 void Simpson::greeting() {
9:	   cout << "hello!";
10:	 }
11:	 
12:	 void Simpson::parting() {
13:	   cout << "goodbye!";
14:	 }
15:	 
16:	 class Bart : public Simpson {
17:	   void greeting();
18:	   void catchPhrase();
19:	   void parting();
20:	 }
21:	 
22:	 void Bart::greeting() {
23:	   cout << "Hi, I'm Bart!";
24:	 }
25:	 
26:	 void Bart::catchPhrase() {
27:	   cout << "Don't have a cow!";
28:	 }
29:	 
30:	 void Bart::parting() {
31:	   cout << "Later!";
32:	 }
33:	 
34:	 class Lisa : public Simpson {
35:	   void greeting();
36:	   void catchPhrase();
37:	 }
38:	 
39:	 void Lisa::greeting() {
40:	   cout << "Hi, my name is Lisa.";
41:	 }
42:	 
43:	 void Lisa::catchPhrase() {
44:	   cout << "I like tai-chi and chai tea";
45:	 }
46:	 
47:	 int main() {
48:	   Simpson s1;
49:	   Simpson* sp1, sp2, sp3;
50:	   Bart b1;  
51:	   Lisa l1;
52:	 
53:	   s1.greeting();
54:	   s1.catchPhrase();
55:	   s1.parting();
56:	 
57:	   b1.greeting();
58:	   l1.catchPhrase();
59:	   b1.parting();
60:	 
61:	   sp1 = &s1;
62:	   sp1->greeting();
63:	   sp1->parting();
64:	 
65:	   sp2 = &l1;
66:	   sp2->greeting();
67:	   sp2->catchPhrase();
68:	   sp2->parting();
69:	 
70:	   sp3 = &b1;
71:	   sp3->greeting();
72:	   sp3->catchPhrase();
73:	   sp3->parting();  
74:	 }

1. What lines are printed out by main()?
2. Which are the inherited functions, virtual functions and pure virutal functions? What's the difference?
3. How would you make Simpson into an abstract class?

Programming Assignment 2

• Your name
• Your SID
• Your partner's name
• Your partner's SID
• How many hours you spent on the project

make clean
handin cs40at pa2 *