C++ Programming Code Examples
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Virtual functions: interface class
/* Virtual functions: interface class */
#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;
}
The pointer in C++ language is a variable, it is also known as locator or indicator that points to an address of a value. In C++, a pointer refers to a variable that holds the address of another variable. Like regular variables, pointers have a data type. For example, a pointer of type integer can hold the address of a variable of type integer. A pointer of character type can hold the address of a variable of character type. You should see a pointer as a symbolic representation of a memory address. With pointers, programs can simulate call-by-reference. They can also create and manipulate dynamic data structures. In C++, a pointer variable refers to a variable pointing to a specific address in a memory pointed by another variable.
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
In C++, constructor is a special method which is invoked automatically at the time of object creation. It is used to initialize the data members of new object generally. The constructor in C++ has the same name as class or structure. Constructors are special class functions which performs initialization of every object. The Compiler calls the Constructor whenever an object is created. Constructors initialize values to object members after storage is allocated to the object. Whereas, Destructor on the other hand is used to destroy the class object. • Default Constructor: A constructor which has no argument is known as default constructor. It is invoked at the time of creating object.
In while loop, condition is evaluated first and if it returns true then the statements inside while loop execute, this happens repeatedly until the condition returns false. When condition returns false, the control comes out of loop and jumps to the next statement in the program after while loop. The important point to note when using while loop is that we need to use increment or decrement statement inside while loop so that the loop variable gets changed on each iteration, and at some point condition returns false. This way we can end the execution of while loop otherwise the loop would execute indefinitely. A while loop that never stops is said to be the infinite while loop, when we give the condition in such a way so that it never returns false, then the loops becomes infinite and repeats itself indefinitely.
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