Hello World

1 #include <iostream>
2 
3 int main()
4 {
5   std::cout << "Hello World!" << std::endl;
6   return 0; // Must return an integer (int main)
7 }

Line 1: #include <iostream>
Lines beginning with a hash sign (#) are directives read and interpreted by what is known as the preprocessor. They are special lines interpreted before the compilation of the program itself begins. In this case, the directive #include <iostream>, instructs the preprocessor to include a section of standard C++ code, known as header iostream, that allows to perform standard input and output operations, such as writing the output of this program (Hello World) to the screen.

Line 5: std::cout << "Hello World!" << std::endl;
This statement has three parts: First, std::cout, which identifies the Standard Character output Device (usually, this is the computer screen). Second, the insertion operator (<<), which indicates that what follows is inserted into std::cout. Finally, a sentence within quotes ("Hello world!"), is the content inserted into the standard output.

Note one doesn't have to use the :: (namespace) operator, if need be one can set a using directive for the namespace so everything contained within the namespace is accessible directly from the scope of the file.

1 #include <iostream>
2 using namespace std;
3 
4 int main()
5 {
6   cout << "Hello World!" << std::endl;
7   return 0; // Must return an integer (int main)
8 }

in this case std::cout is no longer required & one can just use the keyword cout.