Class Declaration and Principles of C++ Inheritance and Casting

1. CIS 230 29-Mar-06

2. Quiz • Write a class declaration (what would go in our Coord.h file…) for the class Coord that contains: • T private floating-point data members named xval and yval. • S Constructor function that does not receive any arguments. • A display function named printCoord() that does not accept or return any arguments. • A friend function named ConvPolar() that accepts two floating point numbers and returns a Coord.

3. Overview • Cast • Inheritance • Protected • Inheritance Overriding • #include “ “ • File Management

4. Cast • Temporarily converts one data type to another • Example: int first, second; float answer; … answer = (first + second) / 2; answer = (first + second) / 2.0; answer = ( (float) first + (float) second ) / 2; Integer division Real division Real Division Cast to a float

5. Cast • Two different ways to cast: • (float) first • float (first) • Example • answer = first / second; • Integer division • Can’t just add a decimal point • answer = (float) first / (float) second;

6. Inheritance • A class may be defined in terms of a previously defined class • This new class has all the components of its parent class: • Data • Methods • The new class may then add features of its own.

7. quadrilateral parallelogram trapezoid rectangle rhombus Inheritance • Each class may have many direct descendants Rhombus “inherits” all the aspects of parallelogram AND ALSO all the aspects of quadrilateral

8. Subclass form class Name : access Parent_class { … … }; Usually Public

9. Circle & Cylinder Circle Cylinder Sphere

10. Circle class class Circle { private: float radius; public: void store_radius(float); float calc_circum(); float calc_area(); float return_radius(); };

11. Cylinder class class Cylinder : public Circle { private: float length; public: void store_length(float); float clac_volume(); float return_length(); };

12. Cylinder member functions void Cylinder::store_length(float lnth) { length = lnth; } float Cylinder::calc_volume(void) { return (length * calc_area()); } Invokes on of its “parent’s” methods

13. Main() int main() { Cylinder cyl; float answer; cyl.store_radius(3); cyl.store_length(10); answer = cyl.calc_volume(); cout << "The volume of the cylinder is " << answer << '\n'; return 0; }

14. Problem • Cylinder HAS a radius (inherited) • Cylinder cannot directly touch it float Cylinder::calc_volume() { return (3.14 * radius * radius * length); } This is cylinder’s radius, but it was declared private in Circle

15. Protected • Protected – A new access form • Pivate to the outside world • Allows descendent classes access • Use in the original class class Circle { protected: float radius; public: … }; It’s important to PLAN your class hierarchy

16. Inheritance Overriding • To override a parent method: • Write a new method with the same name • Example: • Assume we want Cylinder’s area to be its entire surface area

17. Cylinder class class Cylinder : public Circle { private: float length; public: void store_length(float); float clac_volume(); float return_length(); float calc_area(); } Same name as in Circle

18. Cylinder::calc_area() float cylinder::calc_area() { float end, side; end = 3.14 * radius * radius; side = 2 * 3.14 * radius * length; return (2 * end + side); } This creates a problem in cylinder’s original calc_volume().

19. Cylinder::calc_volume() float Cylinder::calc_volume() { return (length * Circle::calc_area()); } Uses the parent method

20. #include “ “ • Classes (or other functions) may be used by other programs • Important to have a good class hierarchy • Important to have private/protected/public set correctly • #include “filename.ext” • Searches in the same directory as the program being compiled • Source code that will be compiled with the program • Should be thoroughly tested

21. We already know… • Circle.h contains: class Circle { protected: //variable declarations public: //method prototypes } • Circle.cpp would contain: • #include “circle.h” • method definitions

22. Descending with #include “ “ • In Cylinder.h: • #include “circle.h” • In main.cpp • #include “cylinder.h”

23. File Management circle.h cylinder.h #include “circle.h” main.cpp #include “cylinder.h” circle.cpp #include “circle.h” cylinder.cpp #include “cylinder.h”