C++ Programming Code Examples
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Demonstrate virtual functons: list interface
/* Demonstrate virtual functons: list interface */
#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 queueObject;
p = &queueObject; // 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 stackObject;
p = &stackObject; // 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;
}
A C++ virtual function is a member function in the base class that you redefine in a derived class. It is declared using the virtual keyword. It is used to tell the compiler to perform dynamic linkage or late binding on the function. There is a necessity to use the single pointer to refer to all the objects of the different classes. So, we create the pointer to the base class that refers to all the derived objects. But, when base class pointer contains the address of the derived class object, always executes the base class function. This issue can only be resolved by using the 'virtual' function. A 'virtual' is a keyword preceding the normal declaration of a function.
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.
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code.
Deallocate storage space. Default deallocation functions (single-object form). A delete operator is used to deallocate memory space that is dynamically created using the new operator, calloc and malloc() function, etc., at the run time of a program in C++ language. In other words, a delete operator is used to release array and non-array (pointer) objects from the heap, which the new operator dynamically allocates to put variables on heap memory. We can use either the delete operator or delete [ ] operator in our program to delete the deallocated space. A delete operator has a void return type, and hence, it does not return a value.
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.
Allocate storage space. Default allocation functions (single-object form). A new operator is used to create the object while a delete operator is used to delete the object. When the object is created by using the new operator, then the object will exist until we explicitly use the delete operator to delete the object. Therefore, we can say that the lifetime of the object is not related to the block structure of the program.
LIFO stack. Stacks are a type of container adaptor, specifically designed to operate in a LIFO context (last-in first-out), where elements are inserted and extracted only from one end of the container. stacks are implemented as container adaptors, which are classes that use an encapsulated object of a specific container class as its underlying container, providing a specific set of member functions to access its elements. Elements are pushed/popped from the "back" of the specific container, which is known as the top of the stack.
The main purpose of C++ programming is to add object orientation to the C programming language and classes are the central feature of C++ that supports object-oriented programming and are often called user-defined types. A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class.
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
The exit function terminates the program normally. Automatic objects are not destroyed, but static objects are. Then, all functions registered with atexit are called in the opposite order of registration. The code is returned to the operating system. An exit code of 0 or EXIT_SUCCESS means successful completion. If code is EXIT_FAILURE, an indication of program failure is returned to the operating system. Other values of code are implementation-defined. Calls all functions registered with the atexit() function, and destroys C++ objects with static storage duration, all in last-in-first-out (LIFO) order. C++ objects with static storage duration are destroyed in the reverse order of the completion of their constructor. (Automatic objects are not destroyed as a result of calling exit().)
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement, The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
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