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==Demonstrating composition--an object with member objects==

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

==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>
<pre class=codeResult>Values in ob1 are 9 and 7
Values in ob2 are 2 and 5</pre>

==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>
<pre class=codeResult>Area: 3000
20</pre>

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