STRUCTURE OF C++ PROGRAM

STRUCTURE OF C++ PROGRAM

#include<header file>
main ()
{
...........
...........
...........
}
A C++ program starts with function called main ( ). The body of the function is enclosed between curly braces. The program statements are written within the braces. Each statement must end by a semicolon;(statement terminator). A C++ program may contain as many functions as required. However, when the program is loaded in the memory, the control is handed over to function main ( ) and it is the first function to be executed.

// This is my first program is C++
/* this program will illustrate different components of
a simple program in C++ */

# include <iostream.h>
int main ( )
{
   cout <<"Hello World!";
   return 0;
} When the above program is compiled, linked and executed, the following output is displayed on the VDU screen.
Hello World!
Various components of this program are discussed below:

Comments

First three lines of the above program are comments and are ignored by the compiler. Comments are included in a program to make it more readable. If a comment is short and can be accommodated in a single line, then it is started with double slash sequence in the first line of the program. However, if there are multiple lines in a comment, it is enclosed between the two symbols /* and */

#include <iostream.h>

The line in the above program that start with # symbol are called directives and are instructions to the compiler. The word include with '#' tells the compiler to include the file iostream.h into the file of the above program. File iostream.h is a header file needed for input/ output requirements of the program. Therefore, this file has been included at the top of the program.

int main ( )

The word main is a function name. The brackets ( ) with main tells that main ( ) is a function. The word int before main ( ) indicates that integer value is being returned by the function main (). When program is loaded in the memory, the control is handed over to function main ( ) and it is the first function to be executed.

Curly bracket and body of the function main ( )

A C++ program starts with function called main(). The body of the function is enclosed between curly braces. The program statements are written within the brackets. Each statement must end by a semicolon, without which an error message in generated.

cout<<"Hello World!";

This statement prints our "Hello World!" message on the screen. cout understands that anything sent to it via the << operator should be printed on the screen.

return 0;

This is a new type of statement, called a return statement. When a program finishes running, it sends a value to the operating system. This particular return statement returns the value of 0 to the operating system, which means “everything went okay!”.
/* This program illustrates how to
declare variable, read data and display data. */

#include <iostream.h>
int main()
{
   int rollno; //declare the variable rollno of type int
   float marks; //declare the variable marks of type float
   cout << "Enter roll number and marks :";
   cin >> rollno >> marks; //store data into variable rollno & marks
   cout << "Rollno: " << rollno<<"\n";
   cout << "Marks: " << marks;
   return 0;
} Sample Run: In this sample run, the user input is shaded.
Enter roll number and marks :102 87.5
Rollno: 102
Marks: 87.5