C++ Tutorial/Class/class definition

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classes example

<source lang="cpp">#include <iostream>

  1. include <stdio.h>

using namespace std; class Rectangle { 

   int x, y;
 public:
   void set_values (int,int);
   int area (void) {return (x*y);}

}; void Rectangle::set_values (int a, int b) { 

 x = a;
 y = b;

} int main () { 

 Rectangle rect;
 rect.set_values (3,4);
 cout << "area: " << rect.area();
 return 0;

}</source> 

area: 12"

Class objects can be assigned to each other using default memberwise assignment

<source lang="cpp">#include <iostream> using std::cout; using std::endl; class Date { public: 

  Date( int = 1, int = 1, int = 2007 );
  void print();

private: 

  int month;
  int day;
  int year;

}; Date::Date( int m, int d, int y ) { 

  month = m;
  day = d;
  year = y;

} void Date::print() { 

  cout << month << "/" << day << "/" << year;

} int main() { 

  Date date1( 8, 8, 2008 );
  Date date2;
  cout << "date1 = ";
  date1.print();
  cout << "\ndate2 = ";
  date2.print();
  date2 = date1;
  cout << "\n\nAfter default memberwise assignment, date2 = ";
  date2.print();
  cout << endl;
  return 0;

}</source> 

date1 = 8/8/2008
date2 = 1/1/2007
After default memberwise assignment, date2 = 8/8/2008

containership with employees and degrees

<source lang="cpp">#include <iostream> 

 #include <string>  
 using namespace std;  
 class student{  
    private:  
       string school; 
       string degree; 
    public:  
       void getedu(){  
          cout << "   Enter name of school or university: ";  
          cin >> school;  
          cout << "   Enter highest degree earned \n";  
          cout << "   (Highschool, Bachelor"s, Master"s, PhD): ";  
          cin >> degree;  
       }  
       void putedu() const{  
          cout << "\n   School or university: " << school;  
          cout << "\n   Highest degree earned: " << degree;  
       }  
 };  
 class employee{  
    private:  
       string name; 
       unsigned long number;  
    public:  
       void getdata(){  
          cout << "\n   Enter last name: "; cin >> name;  
          cout << "   Enter number: ";      cin >> number;  
       }  
       void putdata() const{  
          cout << "\n   Name: " << name;  
          cout << "\n   Number: " << number;  
       }  
 };  
 class manager{  
    private:  
       string title;   
       double dues;    
       employee emp;   
       student stu;    
    public:  
       void getdata(){  
          emp.getdata();  
          cout << "   Enter title: ";          cin >> title;  
          cout << "   Enter golf club dues: "; cin >> dues;  
          stu.getedu();  
       }  
       void putdata() const{  
          emp.putdata();  
          cout << "\n   Title: " << title;  
          cout << "\n   Golf club dues: " << dues;  
          stu.putedu();  
       }  
 };  
 class scientist{  
    private:  
       int pubs;
       employee emp;
       student stu; 
    public:  
       void getdata(){  
          emp.getdata();  
          cout << "   Enter number of pubs: "; cin >> pubs;  
          stu.getedu();  
       }  
       void putdata() const{  
          emp.putdata();  
          cout << "\n   Number of publications: " << pubs;  
          stu.putedu();  
       }  
   };  
 class laborer{  
    private:   
       employee emp;
    public:  
       void getdata(){ emp.getdata(); }  
       void putdata() const{ emp.putdata(); }  
 };  
 int main()  
 {  
    manager m1;  
    scientist s1, s2;  
    laborer l1;  
   
    cout << endl;  
    cout << "\nEnter data for manager 1";    
    m1.getdata();                            
   
    cout << "\nEnter data for scientist 1";  
    s1.getdata();  
   
    cout << "\nEnter data for scientist 2";  
    s2.getdata();  
   
    cout << "\nEnter data for laborer 1";  
    l1.getdata();  
   
    cout << "\nData on manager 1";           
    m1.putdata();                            
   
    cout << "\nData on scientist 1";  
    s1.putdata();  
   
    cout << "\nData on scientist 2";  
    s2.putdata();  
   
    cout << "\nData on laborer 1";  
    l1.putdata();  
    cout << endl;  
    return 0;  
 }</source>

Create an object from a Class and call its function

<source lang="cpp">#include <iostream> using std::cout; using std::endl; class MyClass { public: 

  void displayMessage()
  {
     cout << "Welcome!" << endl;
  }

}; int main() { 

  MyClass obj; 
  obj.displayMessage(); 
  return 0;

}</source> 

Welcome!

Define a class with a member function that takes a parameter

<source lang="cpp">#include <iostream> using std::cout; using std::cin; using std::endl;

  1. include <string>

using std::string; using std::getline; class MyClass { public: 

  void displayMessage( string n )
  {
     cout << "Welcome \n" << n << "!" 
        << endl;
  }

}; int main() { 

  string name; 
  MyClass obj;
  
  cout << "Please enter the name:" << endl;
  getline( cin, name );
  cout << endl;
  obj.displayMessage( name );
  return 0;

}</source> 

Please enter the name:
Joe
Welcome
Joe!

Define class to record time

<source lang="cpp">#include <iomanip>

  1. include <iostream>

using std::cout; using std::endl; using std::setfill; using std::setw; class Time { public: 

  Time(); 
  void setTime( int, int, int );
  void printUniversal();
  void printStandard();

private: 

  int hour;
  int minute;
  int second;

}; Time::Time() { 

  hour = minute = second = 0;

} void Time::setTime( int h, int m, int s ) { 

  hour = h ;
  minute = m;
  second = s ;

} void Time::printUniversal() { 

  cout << setfill( "0" ) << setw( 2 ) << hour << ":" << setw( 2 ) << minute << ":" << setw( 2 ) << second;

} void Time::printStandard() { 

  cout << ( ( hour == 0 || hour == 12 ) ? 12 : hour " 
     << setfill( "0" ) << setw( 2 ) << minute << ":" << setw( 2 )
     << second << ( hour < 12 ? " AM" : " PM" );

} int main() { 

  Time t; 
  t.printUniversal();
  t.printStandard(); 
  t.setTime( 1, 2, 6 ); 
  t.printUniversal();
  t.printStandard(); 
  t.setTime( 99, 99, 99 ); 
  t.printUniversal();
  t.printStandard();
  return 0;

}</source> 

00:00:0012:00:00 AM01:02:061:02:06 AM99:99:993:99:99 PM

Define class with a data member and member functions to set and get its value

<source lang="cpp">#include <iostream> using std::cout; using std::cin; using std::endl;

  1. include <string>

using std::string; using std::getline; class MyClass { public: 

  void setName( string name )
  {      
     name = name; 
  }
  
  string getName() 
  {
     return name; 
  } 
  void displayMessage()
  {
     cout << "Welcome to the grade book for\n" << getName() << "!" << endl;
  }

private: 

  string name;

}; int main() { 

  string n; 
  MyClass obj;
  
  cout << "Initial name is: " << obj.getName() << endl;
  cout << "\nPlease enter the name:" << endl;
  getline( cin, n );
  obj.setName( n );
  cout << endl;
  obj.displayMessage();
  return 0;

}</source> 

Initial name is:
Please enter the name:
Joe
Welcome to the grade book for
!

Define your first class

<source lang="cpp">#include <iostream> using namespace std;


class ThreeDimension { public: 

 int X;   
 int Y;     
 int Z;

};

int main() { 

 ThreeDimension myDimension;  
 int range;  

 // Assign values to fields in myDimension. 
 myDimension.X = 7; 
 myDimension.Y = 16; 
 myDimension.Z = 21; 
 
 // Compute the range assuming a full tank of gas. 
 range = myDimension.Y * myDimension.Z; 
 
 cout << range;  

 return 0;

}</source> 

336

Friend Classes

<source lang="cpp">#include <iostream> using namespace std;

class TwoValues { 

 int a;
 int b;

public: 

 TwoValues(int i, int j) { a = i; b = j; }
 friend class Min;

};

class Min { public: 

 int min(TwoValues x);

};

int Min::min(TwoValues x) { 

 return x.a < x.b ? x.a : x.b;

}

int main() { 

 TwoValues ob(10, 20);
 Min m;
  
 cout << m.min(ob);
  
 return 0;

}</source>

Inner class

<source lang="cpp">#include <iostream> using namespace std; class Outer { 

public:
  Outer(void) 
  { cout << "Just instantiated an outer\n"; 
    outer_data = 2002; 
  };
  class Inner 
  {
    public:
      Inner(void) 
    { 
      cout << "Just instantiated an inner\n"; 
          inner_data = 1001; 
    };
      void show_data(void) { cout << "Inner: " << inner_data << endl; };
    private:
      int inner_data;
  } inside_stuff; 
  void show_all_data(void) 
  { 
    inside_stuff.show_data(); 
      cout << "Outer: " << outer_data << endl; 
  };
private:
  int outer_data;

}; int main(void) { 

  Outer my_data;
  my_data.show_all_data();

}</source>

Instantiating multiple objects of the class using its constructor

<source lang="cpp">#include <iostream> using std::cout; using std::endl;

  1. include <string>

using std::string; class MyClass { public: 

  MyClass( string name )
  {
     setName( name ); 
  } 
  void setName( string n )
  {
     name = n;
  } 
  string getName()
  {
     return name; 
  } 
  void displayMessage()
  {
     cout << "Welcome " << getName()  << "!" << endl;
  }

private: 

  string name;

}; int main() { 

  MyClass obj1( "A" );
  MyClass obj2( "B" );
  cout << obj1.getName()<< "\n" << obj2.getName() << endl;
  return 0;

}</source> 

A
B

Local Classes: A class may be defined within a function

<source lang="cpp">#include <iostream> using namespace std;

void f();

int main() { 

 f();
 return 0;

}

void f() { 

 class myclass {
   int i;
 public:
   void put_i(int n) { i=n; }
   int get_i() { return i; }
 } ob;
  
 ob.put_i(10);
 cout << ob.get_i();

}</source>

Источник — «http://cppe.ru/index.php?title=C%2B%2B_Tutorial/Class/class_definition&oldid=2322»