Basically a C++ program involves the following section:
C++ Program which Outputs a Line of Text
/*
* File: main.cpp
* Author: Gautam
* Created on October 16, 2011, 4:09 PM
*/
#include <iostream>
int main()
{
std::cout<<"This is my first C++ Program.";
std::cout<<std::endl<<"and its very easy";
}
Run
Click on the “Run” button to see how it works.
Program Output:
Let’s look into various parts of the above C++ program:
| /* Comments */ | Comments are a way of explaining what makes a program. Comments are ignored by the compiler and used by others to understand the code. |
| #include <iostream> | is a preprocessor directive. It tells the preprocessor to include the contents of iostream header file in the program before compilation. This file is required for input output statements. |
| int/void | int/void is a return value, which will be explained in a while. |
| main() | The main() is the main function where program execution begins. Every C++ program should contain only one main function. |
| Braces | Two curly brackets “{…}” are used to group all statements together. |
std::cout<<"This is my first C++ Program";
The above line is a statement in C++. A statement must always terminate with a semicolon (;) otherwise it causes a syntax error. This statement introduces two new features of C++ language, cout and << operator.
You will also notice that the words are inside inverted commas because they are what is called a string. Each letter is called a character and a series of characters that is grouped together is called a string. Strings must always be put between inverted commas.
We used std:: before cout. This is required when we use #include <iostream> .
It specifies that we are using a name (cout) which belongs to namespace std. Namespace is a new concept introduced by ANSI C++ which defines the scope of identifiers which are used in the program. std is the namespace where C++ standard libraries are defined.
Operator << is the insertion stream operator. It sends contents of variable on its right to the object on its left. In our case, right operand is the string “This is my first c++ Program” and left operand is cout object. So it sends the string to the cout object and cout object then displays it on the output screen.
namespace
using namespace std;
If you specify using namespace std then you don’t have to put std:: throughout your code. The program will know to look in the std library to find the object. Namespace std contains all the classes, objects and functions of the standard C++ library.
Example:
/*
* File: main.cpp
* Author: Gautam
* Created on October 16, 2011, 4:09 PM
*/
#include <iostream>
using namespace std;
int main()
{
cout<<"This is my first C++ Program.";
cout<<std::endl<<"and its very easy";
}
Run
Click on the “Run” button to see how it works.
Return Statement
| return 0 | At the end of the main function returns value 0. |
In new C++ you have to use:
void main() and iostream.h is only valid for Turbo C++.