C++ Tutorial/Class/class combination

Demonstrating composition--an object with member objects

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

1. include <cstring>

using std::strlen; using std::strncpy;

class Date { public:

  Date( int = 1, int = 1, int = 1900 );
  void print() const; 
  ~Date(); 

private:

  int month; 
  int day; 
  int year;

}; Date::Date( int mn, int dy, int yr ) {

  month = mn;
  year = yr;
  day = dy );

} void Date::print() const {

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

} Date::~Date() {

  cout << "Date object destructor for date ";
  cout << endl;

} class Employee { public:

  Employee( const char * const, const char * const, 
     const Date &, const Date & );
  void print() const;
  ~Employee();

private:

  char firstName[ 25 ];
  char lastName[ 25 ];
  const Date birthDate; 
  const Date hireDate; 

}; Employee::Employee( const char * const first, const char * const last,const Date &dateOfBirth, const Date &dateOfHire )

  : birthDate( dateOfBirth ), hireDate( dateOfHire ) 

{

  strcpy( firstName, first);
  strcpy( lastName, last);

} void Employee::print() const {

  cout << lastName << ", " << firstName << "  Hired: ";
  hireDate.print();
  cout << "  Birthday: ";
  birthDate.print();
  cout << endl;

} Employee::~Employee() {

  cout << "Employee destructor: " << lastName << ", " << firstName << endl;

} int main() {

  Date birth( 7, 24, 1949 );
  Date hire( 3, 12, 1989 );
  Employee manager( "A", "B", birth, hire );
  cout << endl;
  manager.print();
  return 0;

}</source>

B, A  Hired: 3/12/1989  Birthday: 7/24/1949
Employee destructor: B, A
Date object destructor for date
Date object destructor for date
Date object destructor for date
Date object destructor for date

Initialize inner object using initialization syntax

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

class IntPair { public:

 int a;  
 int b;  
 
 IntPair(int i, int j) : a(i), b(j) { }  

};

class MyClass {

 IntPair nums;

public:

 MyClass(int x, int y) : nums(x,y) { }  
 
 int getNumA() { return nums.a; }  
 int getNumB() { return nums.b; }  

};

int main() {

 MyClass ob1(7, 9), ob2(5, 2);  
 
 cout << "Values in ob1 are " << ob1.getNumB() << 
         " and " << ob1.getNumA() << endl;  
 
 cout << "Values in ob2 are " << ob2.getNumB() << 
         " and " << ob2.getNumA() << endl; 
  
 return 0;  

}</source>

Values in ob1 are 9 and 7
Values in ob2 are 2 and 5

Use class as a member field

<source lang="cpp">#include <iostream> class Point // holds x,y coordinates {

   // no constructor, use default

public:

   void SetX(int x) { itsX = x; }
   void SetY(int y) { itsY = y; }
   int GetX()const { return itsX;}
   int GetY()const { return itsY;}

private:

   int itsX;
   int itsY;

};// end of Point class declaration

class Rectangle { public:

   Rectangle (int top, int left, int bottom, int right);
   ~Rectangle () {}
   int GetTop() const { return itsTop; }
   int GetLeft() const { return itsLeft; }
   int GetBottom() const { return itsBottom; }
   int GetRight() const { return itsRight; }
   Point  GetUpperLeft() const { return itsUpperLeft; }
   Point  GetLowerLeft() const { return itsLowerLeft; }
   Point  GetUpperRight() const { return itsUpperRight; }
   Point  GetLowerRight() const { return itsLowerRight; }
   void SetUpperLeft(Point Location);
   void SetLowerLeft(Point Location);
   void SetUpperRight(Point Location);
   void SetLowerRight(Point Location);
   void SetTop(int top);
   void SetLeft (int left);
   void SetBottom (int bottom);
   void SetRight (int right);
   int GetArea() const;

private:

   Point  itsUpperLeft;
   Point  itsUpperRight;
   Point  itsLowerLeft;
   Point  itsLowerRight;
   int    itsTop;
   int    itsLeft;
   int    itsBottom;
   int    itsRight;

};

Rectangle::Rectangle(int top, int left, int bottom, int right) {

   itsTop = top;
   itsLeft = left;
   itsBottom = bottom;
   itsRight = right;
   itsUpperLeft.SetX(left);
   itsUpperLeft.SetY(top);
   itsUpperRight.SetX(right);
   itsUpperRight.SetY(top);
   itsLowerLeft.SetX(left);
   itsLowerLeft.SetY(bottom);
   itsLowerRight.SetX(right);
   itsLowerRight.SetY(bottom);

} void Rectangle::SetUpperLeft(Point Location) {

   itsUpperLeft = Location; 
   itsUpperRight.SetY(Location.GetY());
   itsLowerLeft.SetX(Location.GetX());
   itsTop = Location.GetY();
   itsLeft = Location.GetX();

} void Rectangle::SetLowerLeft(Point Location) {

   itsLowerLeft = Location; 
   itsLowerRight.SetY(Location.GetY());
   itsUpperLeft.SetX(Location.GetX());
   itsBottom = Location.GetY();
   itsLeft = Location.GetX();

} void Rectangle::SetLowerRight(Point Location) {

   itsLowerRight = Location; 
   itsLowerLeft.SetY(Location.GetY());
   itsUpperRight.SetX(Location.GetX());
   itsBottom = Location.GetY();
   itsRight = Location.GetX();

} void Rectangle::SetUpperRight(Point Location) {

   itsUpperRight = Location; 
   itsUpperLeft.SetY(Location.GetY());
   itsLowerRight.SetX(Location.GetX());
   itsTop = Location.GetY();
   itsRight = Location.GetX();

} void Rectangle::SetTop(int top) {

   itsTop = top;
   itsUpperLeft.SetY(top);
   itsUpperRight.SetY(top);

} void Rectangle::SetLeft(int left) {

   itsLeft = left;
   itsUpperLeft.SetX(left);
   itsLowerLeft.SetX(left);

} void Rectangle::SetBottom(int bottom) {

   itsBottom = bottom;
   itsLowerLeft.SetY(bottom);
   itsLowerRight.SetY(bottom);

} void Rectangle::SetRight(int right) {

   itsRight = right;
   itsUpperRight.SetX(right);
   itsLowerRight.SetX(right);

} int Rectangle::GetArea() const {

   int Width = itsRight-itsLeft;
   int Height = itsTop - itsBottom;
   return (Width * Height);

} int main() {

   Rectangle MyRectangle (100, 20, 50, 80 );
   int Area = MyRectangle.GetArea();
   std::cout << "Area: " << Area << "\n";
   std::cout << MyRectangle.GetUpperLeft().GetX();
   return 0;

}</source>

Area: 3000
20