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Introduction to Object Oriented Programming (Continued)

Introduction to Object Oriented Programming (Continued). Cats. 1. Objectives. You will be able to: Write and use classes with multiple member variables. Use the "this" pointer in methods. Use "const" correctly in various places within a method declaration. Understand #pragma once. 2.

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Introduction to Object Oriented Programming (Continued)

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  1. Introduction to Object Oriented Programming(Continued) Cats 1

  2. Objectives You will be able to: • Write and use classes with multiple member variables. • Use the "this" pointer in methods. • Use "const" correctly in various places within a method declaration. • Understand #pragma once 2

  3. Class Cat • Let's create a class to represent cats. • Perhaps for use in a veterinarian's office. • Each cat has: • Name (Up to 20 letters) • Weight • Date of birth

  4. New Project • Create a new C++ console project in Visual Studio.

  5. New Project

  6. New Project

  7. Add main

  8. Start with a Stub Build and run

  9. Program Running We have a working program!

  10. Add Class Cat

  11. Add Class Cat

  12. Add Class Cat

  13. Class Cat

  14. #pragma once • Same as the traditional guard: #ifndef CAT_H #define CAT_H ... // Definition of class Cat ... #endif • Not ISO Standard C++, but widely supported by current compilers.

  15. Add Member Variables • Each cat has: • Name (Up to 20 letters) • Weight • Date of birth • For Name, use a C string (array of char.) • For Weight, use a double. • What about Date of Birth?

  16. Date of Birth • The C standard library has a way to represent date/time values and functions to manipulate them. • But it's complicated • Let's define a simple, easy to use, struct to represent dates in a user-friendly form: • Day • Month • Year

  17. Cat.h #pragma once struct Date { int Day; int Month; int Year; }; class Cat { private: char name[21]; Date date_of_birth; double weight; public: Cat(void); ~Cat(void); };

  18. Constructor • Add to Cat.h: Cat(const char* name_, Date dob, double weight_); • Why const? • Makes name_ a read-only pointer. • Guarantees that the function will not modify the string that is passed as that argument. • DOES NOT mean that the argument has to be a constant.

  19. Cat.cpp #include <cstring> #include "Cat.h" Cat::Cat(const char* name_, Date dob, double weight_) { strncpy(this->name, name_, 20); this->name[20] = 0; this->date_of_birth = dob; this->weight = weight_; } Cat::~Cat(void) { }

  20. The "this" Pointer • In any C++ method, the keyword this is a pointer to the object through which the method was called. • Not necessary in this case • Or most cases. • Program would compile the same without it. • Build the project

  21. A Bogus Warning

  22. Suppressing the Warning #define _CRT_SECURE_NO_WARNINGS #include <cstring> #include "Cat.h" Cat::Cat(const char* name_, Date dob, double weight_) { • The #define must the first line of the file in order to suppress Visual Studio's warning about strncpy. Build and run.

  23. Program Running

  24. Accessor Functions • We can create Cat objects now, but we can't do anything with them. • To make the attributes of a Cat visible outside the class, create public we need to provide accessor functions. • Functions that just return the value of a member variable.

  25. Accessor Functions public: Cat(const char* name_, Date dob, double weight_); const char* Name() const { return name;}; Date Date_of_Birth() const { return date_of_birth;}; double Weight() const {return weight;}; ~Cat(void); }; • What are all those const's ? • Note that we are putting the implementation of the methods in the class definition. • Functions will be compiled in line.

  26. main.cpp #include <iostream> #include "Cat.h" using namespace std; int main() { cout << "This is program Cats\n"; Date dob = {12,1,2008}; Cat Fluffy("Fluffy", dob, 8.4); cout << "Cat: " << Fluffy.Name() << " "; cout << "DoB: " << Fluffy.Date_of_Birth().Month << "/" << Fluffy.Date_of_Birth().Day << "/" << Fluffy.Date_of_Birth().Year << " "; cout << "Weight: " << Fluffy.Weight(); cin.get(); // Hold the window open. return 0; }

  27. Program Running

  28. Display Method • We normally want a method in each class that outputs the member variables to the screen. • Add a new public method to Cat.h: void Display() const;

  29. In Cat.cpp #define _CRT_SECURE_NO_WARNINGS #include <cstring> #include <iostream> #include "Cat.h" using namespace std; ... void Cat::Display() const { cout << "Cat: " << this->name << " "; cout << "DoB: " << this->date_of_birth.Month << "/" << this->date_of_birth.Day << "/" << this->date_of_birth.Year << " "; cout << "Weight: " << this->weight << endl; }

  30. main.cpp #include <iostream> #include "Cat.h" using namespace std; int main() { cout << "This is program Cats\n"; Date dob = {12,1,2008}; Cat Fluffy("Fluffy", dob, 8.4); … Fluffy.Display(); cout << endl; cin.get(); // Hold window open. return 0; } Build and run.

  31. Program Running

  32. Assignment • Do today's example for yourself • if you have not done it in class. • Read Chapter 10. 32 End of Presentation

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