в 14:21, 25 мая 2010

2010-05-25T14:21:06Z

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2010-05-25T10:25:29Z

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==abstract base class==

<source lang="cpp">
#include <iostream>
using namespace std;
class CPolygon {
protected:
int width, height;
public:
void set_values (int a, int b)
{ width=a; height=b; }
virtual int area (void) =0;
};
class CRectangle: public CPolygon {
public:
int area (void)
{ return (width * height); }
};
class CTriangle: public CPolygon {
public:
int area (void)
{ return (width * height / 2); }
};
int main () {
CRectangle rect;
CTriangle trgl;
CPolygon * ppoly1 = &rect;
CPolygon * ppoly2 = &trgl;
ppoly1->set_values (4,5);
ppoly2->set_values (4,5);
cout << ppoly1->area() << endl;
cout << ppoly2->area() << endl;
return 0;
}

</source>

==Create an abstract class.==

<source lang="cpp">

#include <iostream>
using namespace std;
class area {
double dim1, dim2;
public:
void setarea(double d1, double d2)
{
dim1 = d1;
dim2 = d2;
}
void getdim(double &d1, double &d2)
{
d1 = dim1;
d2 = dim2;
}
virtual double getarea() = 0; // pure virtual function
};
class rectangle : public area {
public:
double getarea()
{
double d1, d2;

getdim(d1, d2);
return d1 * d2;
}
};
class triangle : public area {
public:
double getarea()
{
double d1, d2;

getdim(d1, d2);
return 0.5 * d1 * d2;
}
};
int main()
{
area *p;
rectangle r;
triangle t;
r.setarea(3.3, 4.5);
t.setarea(4.0, 5.0);
p = &r;
cout << "Rectangle has area: " << p->getarea() << "\n";
p = &t;
cout << "Triangle has area: " << p->getarea() << "\n";
return 0;
}

</source>

==pure virtual members can be called from the abstract base class==

<source lang="cpp">
#include <iostream>
using namespace std;
class CPolygon {
protected:
int width, height;
public:
void set_values (int a, int b)
{ width=a; height=b; }
virtual int area (void) =0;
void printarea (void)
{ cout << this->area() << endl; }
};
class CRectangle: public CPolygon {
public:
int area (void)
{ return (width * height); }
};
class CTriangle: public CPolygon {
public:
int area (void)
{ return (width * height / 2); }
};
int main () {
CRectangle rect;
CTriangle trgl;
CPolygon * ppoly1 = &rect;
CPolygon * ppoly2 = &trgl;
ppoly1->set_values (4,5);
ppoly2->set_values (4,5);
ppoly1->printarea();
ppoly2->printarea();
return 0;
}

</source>

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в 14:21, 25 мая 2010

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