C++ Programming Structure

C++ Programming Structure

Structure of C++

• There are four sections in the structure of C++ program. These sections are as shown in Fig. 1.2.1.

Include file section

Class declaration section

Function definition section

Main function definition

The sample C++ program is as follows ‒

C++ Program

FirstProg.cpp

//This is my first C++ program

//This program simply prints the message Hello World

#include <iostream>

using namespace std;

int main()

{

cout<<"Hello World\n";

}

Execute above program using the g++ command on Linux platform. Note that the gcc package must be installed on your machine to use this command. Following commands must be executed on terminal window.

1) g++ ‒ O First Prog FirstProg.cpp

2) ./FirstProg

program Explanation

The first two lines are the comments. It is a non executable portion.

Then the next line statement begins with the sign #. It is a pre‒processor directive. It tells the pre‒processor to include the header file iostream.h. This specific file iostream.h includes the declarations of the basic standard input‒output library in C++, and it is included because its functionality is going to be used later in the program. In Linux platform # include<iostream> is used.

Next line is

using namespace std;

This statement is used to define scope of the identifiers that are used in the program. std is a namespace where the standard class libraries are defined. By this statement we can bring all the identifiers in the current global scope. The keyword namespace is used to define the scope of identifiers. If namespace is not used then cout statement, must be written as std : : cout.

The void main() is a function from where the execution of C++ program starts. Then { indicates the beginning of the function definition.

The next line starts with cout. The cout represents the standard output stream in C++. By this statement we will get the "Hello world" message printed on the output screen. The cout is declared in standard iostream file. The cout should be followed by << and then by some message in double quotes.

Then the program ends by }.

1. Comments in Program

Comments are those statements in the program which are non executable in nature. They provide simply the information about the programming statements.

There are two ways by which we can give the comments in C++. The First way is similar to the comments in C. The start of the comment is /* and end of the comment is */. This comment statement is a multiline comment statement that means you can comment many lines together using /* and */. Another way is // at the start of the line which is to be commented. This is a single line comment statement .The comment statements are useful in documenting the program.

2. Input and Output Operators

In C++ the input operation is called extraction because data is extracted from keyboard and the operator >> is called extractor.

The C++ statement input operation will be ‒

cin >> a

This input statement on execution will wait for the user to type in a number using keyboard, the value entered by user will then be saved in a variable.

The C++ uses an output operation called insertion because data is inserted or sent from the variable. The operator << is called insertion operator.

The C++ statement for output operation will be ‒

cout << a:

The data contained in variable a will be displayed on the screen.

Example: 1

Write a C++ program to convert the polar co‒ordinates into rectangular co‒ordinates. (Hint: Polar co‒ordinates(radius, angle) and rectangular co‒ordinates(x, y) where x = r*cos(angle) and y = r*sin(angle)).

Solution :

/**************************************************************************

Program to convert the Polar co‒ordinates into rectangular co‒ordinates

**************************************************************************/

#include<iostream>

#include<cmath>

#define PI 3.14159265

using namespace std;

int main()

{

       double r,angle;

       void PolarToRect(double,double);

       cout<<"Enter the value of radius: ":

       cin>>r;

       cout<<"Enter the value of angle(in degree): ";

       cin>>angle;

       PolarToRect(r,angle);

       return 0;

}

void PolarToRect(double r,double angle)

{

       double x,y;

       x=r*cos(angle *PI/180);

       y=r*sin(angle*PI/180);

       cout<<"\nx: "<<<<x;

       cout<<"\ny: "<<y;

       cout<<endl;

}

Output

Enter the value of radius: 5

Enter the value of angle (in degree): 30

x : 4.33013

y : 2.5