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2010-05-25T14:21:06Z

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2010-05-25T10:25:32Z

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==Demonstrate virtual functons: list interface==

<source lang="cpp">
#include <iostream>
#include <cstdlib>
#include <cctype>
using namespace std;
class list {
public:
list *head; // pointer to start of list
list *tail; // pointer to end of list
list *next; // pointer to next item
int num; // value to be stored
list() {
head = tail = next = NULL;
}
virtual void store(int i) = 0;
virtual int retrieve() = 0;
};
class queue : public list {
public:
void store(int i);
int retrieve();
};
void queue::store(int i)
{
list *item;
item = new queue;
if(!item) {
cout << "Allocation error.\n";
exit(1);
}
item->num = i;
if(tail)
tail->next = item;
tail = item;
item->next = NULL;
if(!head)
head = tail;
}
int queue::retrieve()
{
int i;
list *p;
if(!head) {
cout << "List empty.\n";
return 0;
}
// remove from start of list
i = head->num;
p = head;
head = head->next;
delete p;
return i;
}
class stack : public list {
public:
void store(int i);
int retrieve();
};
void stack::store(int i)
{
list *item;
item = new stack;
if(!item) {
cout << "Allocation error.\n";
exit(1);
}
item->num = i;
if(head)
item->next = head;
head = item;
if(!tail)
tail = head;
}
int stack::retrieve()
{
int i;
list *p;
if(!head) {
cout << "List empty.\n";
return 0;
}
// remove from start of list
i = head->num;
p = head;
head = head->next;
delete p;
return i;
}
int main()
{
list *p;
// demonstrate queue
queue q_ob;
p = &q_ob; // point to queue
p->store(1);
p->store(2);
p->store(3);
cout << "Queue: ";
cout << p->retrieve();
cout << p->retrieve();
cout << p->retrieve();
cout << "\n";
// demonstrate stack
stack s_ob;
p = &s_ob; // point to stack
p->store(1);
p->store(2);
p->store(3);
cout << "Stack: ";
cout << p->retrieve();
cout << p->retrieve();
cout << p->retrieve();
cout << "\n";
return 0;
}

</source>

=="Interface" for subclass==

<source lang="cpp">
#include <iostream>
using namespace std;
class AreaClass {
public:
double height;
double width;
};
class Rectangle : public AreaClass {
public:
Rectangle(double h, double w);
double area();
};
class Isosceles : public AreaClass {
public:
Isosceles(double h, double w);
double area();
};
Rectangle::Rectangle(double h, double w)
{
height = h;
width = w;
}
Isosceles::Isosceles(double h, double w)
{
height = h;
width = w;
}
double Rectangle::area()
{
return width * height;
}

double Isosceles::area()
{
return 0.5 * width * height;
}
int main()
{
Rectangle rectangleObject(10.0, 5.0);
Isosceles isoscelesObject(4.0, 6.0);
cout << "Rectangle: " << rectangleObject.area() << endl;
cout << "Triangle: " << isoscelesObject.area() << endl;
return 0;
}

</source>

==Use virtual function to define interface.==

<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()
{
cout << "You must override this function\n";
return 0.0;
}
};
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>

==Virtual functions: interface class==

<source lang="cpp">

#include <iostream>
#include <cstdlib>
using namespace std;
class list {
public:
list *head; // pointer to next item in list
list *tail;
list *next;
int num; // value to be stored
list() {
head = tail = next = NULL;
}
virtual void store(int i) = 0;
virtual int retrieve() = 0;
};
class queue : public list {
public:
void store(int i);
int retrieve();
};
void queue::store(int i)
{
list *item;
item = new queue;
if(!item) {
cout << "Allocation error.\n";
exit(1);
}
item->num = i;
// put on end of list
if(tail)
tail->next = item;
tail = item;
item->next = NULL;
if(!head)
head = tail;
}
int queue::retrieve()
{
int i;
list *p;
if(!head) {
cout << "List empty.\n";
return 0;
}
i = head->num;
p = head;
head = head->next;
delete p;
return i;
}
class stack : public list {
public:
void store(int i);
int retrieve();
};
void stack::store(int i)
{
list *item;
item = new stack;
if(!item) {
cout << "Allocation error.\n";
exit(1);
}
item->num = i;
// put on front of list for stack-like operation
if(head)
item->next = head;
head = item;
if(!tail)
tail = head;
}
int stack::retrieve()
{
int i;
list *p;
if(!head) {
cout << "List empty.\n";
return 0;
}
// remove from start of list
i = head->num;
p = head;
head = head->next;
delete p;
return i;
}
class sorted : public list {
public:
void store(int i);
int retrieve();
};
void sorted::store(int i)
{
list *item;
list *p, *p2;
item = new sorted;
if(!item) {
cout << "Allocation error.\n";
exit(1);
}
item->num = i;
// find where to put next item
p = head;
p2 = NULL;
while(p) { // goes in middle
if(p->num > i) {
item->next = p;
if(p2) p2->next = item; // not 1st element
if(p==head) head = item; // new 1st element
break;
}
p2 = p;
p = p->next;
}
if(!p) { // goes on end
if(tail) tail->next = item;
tail = item;
item->next = NULL;
}
if(!head) // is first element
head = item;
}
int sorted::retrieve()
{
int i;
list *p;
if(!head) {
cout << "List empty.\n";
return 0;
}
// remove from start of list
i = head->num;
p = head;
head = head->next;
delete p;
return i;
}
int main()
{
list *p;
queue q_ob;
p = &q_ob; // point to queue
p->store(1);
p->store(2);
p->store(3);
cout << "Queue: ";
cout << p->retrieve();
cout << p->retrieve();
cout << p->retrieve();
cout << "\n";
stack s_ob;
p = &s_ob; // point to stack
p->store(1);
p->store(2);
p->store(3);
cout << "Stack: ";
cout << p->retrieve();
cout << p->retrieve();
cout << p->retrieve();
cout << "\n";
sorted sorted_ob;
p = &sorted_ob;
p->store(4);
p->store(1);
p->store(3);
p->store(9);
p->store(5);
cout << "Sorted: ";
cout << p->retrieve();
cout << p->retrieve();
cout << p->retrieve();
cout << p->retrieve();
cout << p->retrieve();
cout << "\n";

return 0;
}

</source>

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