C++ Program Structure

The best way to learn a programming language is by writing programs. Typically, the first program beginners write is a program called "Hello World", which simply prints "Hello World" to your computer screen. Although it is very simple, it contains all the fundamental components C++ programs have. Let's look at the code for this program −

int main() {
   std::cout << "Hello World\n";

Let's dissect this program.

Line 1 − We start with the #include<iostream> line which essentially tells the compiler to copy the code from the iostream file(used for managing input and output streams) and paste it in our source file.  Header iostream, that allows performing standard input and output operations, such as writing the output of this program (Hello World) to the screen. Lines beginning with a hash sign (#) are directives read and interpreted by what is known as the preprocessor.

Line 2 − A blank line: Blank lines have no effect on a program.

Line 3 − We then declare a function called main with the return type of int. main() is the entry point of our program. Whenever we run a C++ program, we start with the main function and begin execution from the first line within this function and keep executing each line till we reach the end. We start a block using the curly brace({) here. This marks the beginning of main's function definition, and the closing brace (}) at line 5, marks its end. All statements between these braces are the function's body that defines what happens when main is called.

Line 4 − 

std::cout << "Hello World\n";

This line is a C++ statement. This statement has three parts: First, std::cout, which identifies the standard console output device. Second the insertion operator << which indicates that what follows is inserted into std::cout. Last, we have a sentence within quotes that we'd like printed on the screen. This will become more clear to you as we proceed in learning C++.

In short, we provide cout object with a string "Hello world\n" to be printed to the standard output device.

Note that the statement ends with a semicolon (;). This character marks the end of the statement.