1 C++ Structures Starting to think about objects... - презентация

1 1 C++ Structures Starting to think about objects...

2 Structure A Structure is a container, it can hold a bunch of things. A Structure is a container, it can hold a bunch of things. –These things can be of any type. Structures are used to organize related data (variables) into a nice neat package. Structures are used to organize related data (variables) into a nice neat package. 2

3 Example - Student Record Student Record: Student Record: –Name a string –HW Gradesan array of 3 doubles –Test Gradesan array of 2 doubles –Final Averagea double 3

4 Structure Members Each thing in a structure is called member. Each thing in a structure is called member. Each member has a name, a type and a value. Each member has a name, a type and a value. Names follow the rules for variable names. Names follow the rules for variable names. Types can be any defined type. Types can be any defined type. 4

5 5 Example Structure Definition struct StudentRecord { char *name;// student name double hw[3];// homework grades double test[2];// test grades double ave;// final average };

6 Using a struct By defining a structure you create a new data type. By defining a structure you create a new data type. Once a struct is defined, you can create variables of the new type. Once a struct is defined, you can create variables of the new type. StudentRecord stu; 6

7 Accessing Members You can treat the members of a struct just like variables. You can treat the members of a struct just like variables. You need to use the member access operator '.' (pronounced "dot"): You need to use the member access operator '.' (pronounced "dot"): cout << stu.name << endl; stu.hw[2] = 82.3; stu.ave = total/100; 7

8 8 Structure Assignment You can use structures just like variables: You can use structures just like variables: StudentRecord s1,s2; s1.name = "Joe Student"; … s2 = s1; Copies the entire structure

9 9 Be Careful If a member is a pointer, copying means copying the pointer (not what is pointed to). If a member is a pointer, copying means copying the pointer (not what is pointed to). name ave test hw "Joe Student"

10 10 Probably not what you want StudentRecord s1,s2; s1.name = "Joe Student"; … s2 = s1; s2.name = "Jane Doe"; // now s1.name and s2.name are both // "Jane Doe"

11 11 Pointers to Structures Pointers to structures are used often. Pointers to structures are used often. There is another member access operator used with pointers: -> There is another member access operator used with pointers: -> StudentRecord *sptr; … cout name; cout ave; it looks like a "pointer"!

12 12 Sample Function (won't work!) void update_average( StudentRecord stu) { double tot=0; for (int i=0;i<3;i++) tot += stu.hw[i]; for (int i=0;i<3;i++) tot += stu.test[i]; stu.ave = tot/5; }

13 13 This one works void update_average( StudentRecord *stu) { double tot=0; for (int i=0;i<3;i++) tot += stu->hw[i]; for (int i=0;i<3;i++) tot += stu->test[i]; stu->ave = tot/5; }

14 14 Or use a reference parameter void update_average( StudentRecord &stu) { double tot=0; for (int i=0;i<3;i++) tot += stu.hw[i]; for (int i=0;i<3;i++) tot += stu.test[i]; stu.ave = tot/5; }

15 15 Other stuff you can do with a struct You can also associate special functions with a structure (called member functions). You can also associate special functions with a structure (called member functions). A C++ class is very similar to a structure, we will focus on classes. A C++ class is very similar to a structure, we will focus on classes. –Classes can have (data) members –Classes can have member functions. –Classes can also hide some of the members (functions and data).

16 16 Quick Example struct StudentRecord { char *name; // student name char *name; // student name double hw[3]; // homework grades double hw[3]; // homework grades double test[2]; // test grades double test[2]; // test grades double ave; // final average double ave; // final average void print_ave() { void print_ave() { cout << "Name: " << name << endl; cout << "Name: " << name << endl; cout << "Average: " << ave << endl; cout << "Average: " << ave << endl; }};

17 17 Using the member function doubleStudentRecord stu; … // set values in the structure stu.print_ave();

18 C++ Classes & Object Oriented Programming Exerted from : elearning.najah.edu/OldData/pdfs/C++%20Classes%20Tutorials.ppt

19 Object Oriented Programming Programmer thinks about and defines the attributes and behavior of objects. Programmer thinks about and defines the attributes and behavior of objects. Often the objects are modeled after real- world entities. Often the objects are modeled after real- world entities. Very different approach than function-based programming (like C). Very different approach than function-based programming (like C).

20 Object Oriented Programming Object-oriented programming (OOP) Object-oriented programming (OOP) –Encapsulates data (attributes) and functions (behavior) into packages called classes. So, Classes are user-defined (programmer- defined) types. So, Classes are user-defined (programmer- defined) types. –Data (data members) –Functions (member functions or methods) In other words, they are structures + functions In other words, they are structures + functions

21 Classes in C++ A class definition begins with the keyword class. A class definition begins with the keyword class. The body of the class is contained within a set of braces, { } ; (notice the semi-colon). The body of the class is contained within a set of braces, { } ; (notice the semi-colon). class class_name { …. }; methods Class body (data member + methods) Any valid identifier

22 Classes in C++ Within the body, the keywords private: and public: specify the access level of the members of the class. Within the body, the keywords private: and public: specify the access level of the members of the class. –the default is private. Usually, the data members of a class are declared in the private: section of the class and the member functions are in public: section. Usually, the data members of a class are declared in the private: section of the class and the member functions are in public: section.

23 Classes in C++ class class_name { private: … public: … }; Public members or methods private members or methods

24 Classes in C++ Member access specifiers Member access specifiers –public: can be accessed outside the class directly. can be accessed outside the class directly. –The public stuff is the interface. –private: Accessible only to member functions of class Accessible only to member functions of class Private members and methods are for internal use only. Private members and methods are for internal use only.

25 Class Example This class example shows how we can encapsulate (gather) a circle information into one package (unit or class) This class example shows how we can encapsulate (gather) a circle information into one package (unit or class) class Circle { private: double radius; public: void setRadius(double r); double getDiameter(); double getArea(); double getCircumference(); }; No need for others classes to access and retrieve its value directly. The class methods are responsible for that only. They are accessible from outside the class, and they can access the member (radius)

26 Creating an object of a Class Declaring a variable of a class type creates an object. You can have many variables of the same type (class). Declaring a variable of a class type creates an object. You can have many variables of the same type (class). –Instantiation Once an object of a certain class is instantiated, a new memory location is created for it to store its data members and code Once an object of a certain class is instantiated, a new memory location is created for it to store its data members and code You can instantiate many objects from a class type. You can instantiate many objects from a class type. –Ex) Circle c; Circle *c;

27 Special Member Functions Constructor: Constructor: –Public function member –called when a new object is created (instantiated). –Initialize data members. –Same name as class –No return type –Several constructors Function overloading Function overloading

28 Special Member Functions class Circle { private: double radius; public: Circle(); Circle(int r); void setRadius(double r); double getDiameter(); double getArea(); double getCircumference(); }; Constructor with no argument Constructor with one argument

29 Implementing class methods Class implementation: writing the code of class methods. Class implementation: writing the code of class methods. There are two ways: There are two ways: 1.Member functions defined outside class Using Binary scope resolution operator ( :: ) Using Binary scope resolution operator ( :: ) Ties member name to class name Ties member name to class name Uniquely identify functions of particular class Uniquely identify functions of particular class Different classes can have member functions with same name Different classes can have member functions with same name –Format for defining member functions ReturnType ClassName::MemberFunctionName( ){ …}

30 Implementing class methods 2.Member functions defined inside class –Do not need scope resolution operator, class name; class Circle { private: double radius; public: Circle() { radius = 0.0;} Circle(int r); void setRadius(double r){radius = r;} double getDiameter(){ return radius *2;} double getArea(); double getCircumference(); }; Defined inside class

31 class Circle { private: double radius; public: Circle() { radius = 0.0;} Circle(int r); void setRadius(double r){radius = r;} double getDiameter(){ return radius *2;} double getArea(); double getCircumference(); }; Circle::Circle(int r) { radius = r; } double Circle::getArea() { return radius * radius * (22.0/7); } double Circle:: getCircumference() { return 2 * radius * (22.0/7); } Defined outside class

32 Accessing Class Members Operators to access class members Operators to access class members –Identical to those for struct s –Dot member selection operator (. ) Object Object Reference to object Reference to object –Arrow member selection operator ( -> ) Pointers Pointers

33 class Circle { private: double radius; public: Circle() { radius = 0.0;} Circle(int r); void setRadius(double r){radius = r;} double getDiameter(){ return radius *2;} double getArea(); double getCircumference(); }; Circle::Circle(int r) { radius = r; } double Circle::getArea() { return radius * radius * (22.0/7); } double Circle:: getCircumference() { return 2 * radius * (22.0/7); } void main() { Circle c1,c2(7); cout<

34 class Circle { private: double radius; public: Circle() { radius = 0.0;} Circle(int r); void setRadius(double r){radius = r;} double getDiameter(){ return radius *2;} double getArea(); double getCircumference(); }; Circle::Circle(int r) { radius = r; } double Circle::getArea() { return radius * radius * (22.0/7); } double Circle:: getCircumference() { return 2 * radius * (22.0/7); } void main() { Circle c(7); Circle *cp1 = &c; Circle *cp2 = new Circle(7); cout<

35 Destructors Destructors Destructors –Special member function –Same name as class Preceded with tilde ( ~ ) Preceded with tilde ( ~ ) –No arguments –No return value –Cannot be overloaded –Before system reclaims objects memory Reuse memory for new objects Reuse memory for new objects Mainly used to de-allocate dynamic memory locations Mainly used to de-allocate dynamic memory locations

36 Another class Example This class shows how to handle time parts. This class shows how to handle time parts. class Time { private: int *hour,*minute,*second; public: Time(); Time(int h,int m,int s); void printTime(); void setTime(int h,int m,int s); int getHour(){return *hour;} int getMinute(){return *minute;} int getSecond(){return *second;} void setHour(int h){*hour = h;} void setMinute(int m){*minute = m;} void setSecond(int s){*second = s;} ~Time(); }; Destructor

37 Time::Time() { hour = new int; minute = new int; second = new int; *hour = *minute = *second = 0; } Time::Time(int h,int m,int s) { hour = new int; minute = new int; second = new int; *hour = h; *minute = m; *second = s; } void Time::setTime(int h,int m,int s) { *hour = h; *minute = m; *second = s; } Dynamic locations should be allocated to pointers first

printTime(); t->setHour(7); t->setMinute(17" title="void Time::printTime() { cout<<"The time is : ("<<*hour<<":"<<*minute<<":"<<*second<<")" <printTime(); t->setHour(7); t->setMinute(17" class="link_thumb"> 38 void Time::printTime() { cout<<"The time is : ("<<*hour<<":"<<*minute<<":"<<*second<<")" <printTime(); t->setHour(7); t->setMinute(17); t->setSecond(43); t->printTime(); delete t; } Output: The time is : (3:55:54) The time is : (7:17:43) Press any key to continue Destructor: used here to de- allocate memory locations When executed, the destructor is called printTime(); t->setHour(7); t->setMinute(17"> printTime(); t->setHour(7); t->setMinute(17); t->setSecond(43); t->printTime(); delete t; } Output: The time is : (3:55:54) The time is : (7:17:43) Press any key to continue Destructor: used here to de- allocate memory locations When executed, the destructor is called"> printTime(); t->setHour(7); t->setMinute(17" title="void Time::printTime() { cout<<"The time is : ("<<*hour<<":"<<*minute<<":"<<*second<<")" <printTime(); t->setHour(7); t->setMinute(17">

39 Reasons for OOP 1.Simplify programming 2.Interfaces Information hiding: Information hiding: –Implementation details hidden within classes themselves 3.Software reuse Class objects included as members of other classes Class objects included as members of other classes

40 for(i=0;i<3;i++) for(i=0;i<3;i++) { { for(j=0;j<3;j++) for(j=0;j<3;j++) { { for(m=0;m<3;m++) for(m=0;m<3;m++) { { X[i][j][m]=A[i][m]*B[m][j]; X[i][j][m]=A[i][m]*B[m][j]; C[i][j]+=X[i][j][m]; C[i][j]+=X[i][j][m]; } }

41 Class Activity Write a program to computer an area of a rectangle and triangle using the class concept? Write a program to computer an area of a rectangle and triangle using the class concept?

42 Project

43 How ?

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