C++ is a programming language. This language is so powerful that one can control their computer with it if they want it to. A C++ program is a collection of commands, which tell the computer to do "something". This collection of commands is usually called C++ source code, source code or just code. Commands are either "functions" or "keywords".
Keywords are a basic building block of the language, while functions are, in fact, usually written in terms of simpler functions--you'll see this in our very first program, below. (Confused? Think of it a bit like an outline for a book; the outline might show every chapter in the book; each chapter might have its own outline, composed of sections. Each section might have its own outline, or it might have all of the details written up.) Thankfully, C++ provides a great many common functions and keywords that you can use.
But how does a program actually start? Every program in C++ has one function, always named main , that is always called when your program first executes. From main, you can also call other functions whether they are written by us or, as mentioned earlier, provided by the compiler.
So how do you get access to those prewritten functions? To access those standard functions that comes with the compiler, you include a header with the #include directive . What this does is effectively take everything in the header and paste it into your program.