C++ Programming Code Examples
C++ > Code Snippets Code Examples
Class pointer and virtual function
/* Class pointer and virtual function */
#include <iostream>
using namespace std;
class figure {
protected:
double x, y;
public:
void set_dim(double i, double j=0) {
x = i;
y = j;
}
virtual void show_area() {
cout << "No area computation defined ";
cout << "for this class.\n";
}
} ;
class triangle : public figure {
public:
void show_area() {
cout << "Triangle with height ";
cout << x << " and base " << y;
cout << " has an area of ";
cout << x * 0.5 * y << ".\n";
}
};
class rectangle : public figure {
public:
void show_area() {
cout << "Rectangle with dimensions ";
cout << x << "x" << y;
cout << " has an area of ";
cout << x * y << ".\n";
}
};
class circle : public figure {
public:
void show_area() {
cout << "Circle with radius ";
cout << x;
cout << " has an area of ";
cout << 3.14 * x * x << ".\n";
}
} ;
int main()
{
figure *p; // create a pointer to base type
triangle t; // create objects of derived types
rectangle s;
circle c;
p = &t;
p->set_dim(10.0, 5.0);
p->show_area();
p = &s;
p->set_dim(10.0, 5.0);
p->show_area();
p = &c;
p->set_dim(9.0);
p->show_area();
return 0;
}
The function in C++ language is also known as procedure or subroutine in other programming languages. To perform any task, we can create function. A function can be called many times. It provides modularity and code reusability. Functions are used to provide modularity to a program. Creating an application using function makes it easier to understand, edit, check... Function declaration, is done to tell the compiler about the existence of the function. Function's return type, its name & parameter list is mentioned. Function body is written in its definition. Functions are called by their names. If the function is without argument, it can be called directly using its name. But for functions with arguments, we have two ways to call them:
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.
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.
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.
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.
#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.
Return the least recently inserted item in the queue or throw "Underflow" if empty. Return and remove the least "recently inserted" item from the queue. "Throw Underflow" if empty.
This algorithm takes the input of the number of 'vertex and edges'. Then it takes the input of connected vertex pairs. Print the incidence list representation of the graph. And for each
