could you explain this?

This is a discussion on could you explain this? within the C++ Programming forums, part of the General Programming Boards category; Code: //Listing 14.7. Shape classes. #include <iostream> using std::cout; using std::cin; using std::endl; class Shape { public: Shape(){} virtual ~Shape(){} ...

  1. #1
    left crog... back when? incognito's Avatar
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    could you explain this?

    Code:
    //Listing 14.7. Shape classes.
    
    #include <iostream>
    using std::cout;
    using std::cin;
    using std::endl;
    
    class Shape
    {
    public:
    	Shape(){}
    	virtual ~Shape(){}
    	virtual long GetArea() { return -1; } // error
    	virtual long GetPerim() { return -1; }
    	virtual void Draw() {}
    private:
    };
    
    class Circle : public Shape
    {
    public:
    	Circle(int radius):itsRadius(radius){}
    	~Circle(){}
    	long GetArea() { return 3 * itsRadius * itsRadius; }
    	long GetPerim() { return 6 * itsRadius; }
    	void Draw();
    private:
    	int itsRadius;
    	int itsCircumference;
    };
    
    void Circle::Draw()
    {
    	cout << "Circle drawing routine here!\n";
    }
    
    
    class Rectangle : public Shape
    {
    public:
    	Rectangle(int len, int width):
    	itsLength(len), itsWidth(width){}
    	virtual ~Rectangle(){}
    	virtual long GetArea() { return itsLength * itsWidth; }
    	virtual long GetPerim() {return 2*itsLength + 2*itsWidth; }
    	virtual int GetLength() { return itsLength; }
    	virtual int GetWidth() { return itsWidth; }
    	virtual void Draw();
    private:
    	int itsWidth;
    	int itsLength;
    };
    
    void Rectangle::Draw()
    {
    	for (int i = 0; i<itsLength; i++)
    	{
    		for (int j = 0; j<itsWidth; j++)
    			cout << "x ";
    
    	cout << "\n";
    	}
    }
    
    class Square : public Rectangle
    {
    public:
    	Square(int len);
    	Square(int len, int width);
    	~Square(){}
    	long GetPerim() {return 4 * GetLength();}
    };
    
    Square::Square(int len):
    Rectangle(len,len)
    {}
    
    Square::Square(int len, int width):
    Rectangle(len,width)
    {
    	if (GetLength() != GetWidth())
    	cout << "Error, not a square... a Rectangle??\n";
    }
    
    int main()
    {
    	int choice;
    	bool fQuit = false;
    	Shape * sp;
    
    	while ( !fQuit )
    	{
    		cout << "(1)Circle (2)Rectangle (3)Square (0)Quit: ";
    		cin >> choice;
    
    		switch (choice)
    		{
    		case 0:	fQuit = true;
    				break;
    		case 1: sp = new Circle(5);
    				break;
    		case 2: sp = new Rectangle(4,6);
    				break;
    		case 3: sp = new Square(5);
    				break;
    		default: cout<<"Please enter a number between 0 and 3"<<endl;
    				continue;
    				break;
    		}
    		if( !fQuit )
    			sp->Draw();
    		delete sp;
    		sp = 0;
    		cout << "\n";
    	}
     int exit;cin>>exit;
    	return 0;
    }

    I don't see the defition for the rectangle constructor.....please explain.........
    There are some real morons in this world please do not become one of them, do not become a victim of moronitis. PROGRAMMING IS THE FUTURE...THE FUTURE IS NOW!!!!!!!!!

    "...The only real game I thank in the world is baseball..." --Babe Ruth

    "Life is beautiful"-Don Corleone right before he died.

    "The expert on anything was once a beginner" -Baseball poster I own.


    Left cprog on 1-3-2005. Don't know when I am coming back. Thanks to those who helped me over the years.

  2. #2
    left crog... back when? incognito's Avatar
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    never mind I see it now.....it's just a little bit different that usual (for the book)
    Rectangle(int len, int width):
    itsLength(len), itsWidth(width){}
    There are some real morons in this world please do not become one of them, do not become a victim of moronitis. PROGRAMMING IS THE FUTURE...THE FUTURE IS NOW!!!!!!!!!

    "...The only real game I thank in the world is baseball..." --Babe Ruth

    "Life is beautiful"-Don Corleone right before he died.

    "The expert on anything was once a beginner" -Baseball poster I own.


    Left cprog on 1-3-2005. Don't know when I am coming back. Thanks to those who helped me over the years.

  3. #3
    Registered User
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    I sure am glad you spotted it. It's a bit hidden.

  4. #4
    Code Goddess Prelude's Avatar
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    The author didn't exactly try to hide it, it's where the constructor usually is placed (as the first public method). Of course I would have done it a different way when using an initializer list, either make the definition global and comment so that everything is nice and neat and easy to find:
    Code:
    // Constructor fleshy
    Rectangle::Rectangle(int len, int width): 
      itsLength(len), itsWidth(width)
    {
    }
    or put it all on one line inside the class so that it's easier to read:
    Code:
    Rectangle(int len, int width): itsLength(len), itsWidth(width) {}
    It was probably broken into two lines for space sake, but to some that would make it very difficult to follow, especially people who don't see initializer lists often.

    -Prelude
    My best code is written with the delete key.

  5. #5
    left crog... back when? incognito's Avatar
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    Yeah I guess that's what confused me a bit, because I wasn't really used to see the constructor definition like that.
    There are some real morons in this world please do not become one of them, do not become a victim of moronitis. PROGRAMMING IS THE FUTURE...THE FUTURE IS NOW!!!!!!!!!

    "...The only real game I thank in the world is baseball..." --Babe Ruth

    "Life is beautiful"-Don Corleone right before he died.

    "The expert on anything was once a beginner" -Baseball poster I own.


    Left cprog on 1-3-2005. Don't know when I am coming back. Thanks to those who helped me over the years.

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