Preprocessor Directives

Before we can actually write any meaningful program, we have to learn how to add these standard libraries to our project.

To add external files to your program you have to use preprocessor directives. These are the commands that guide the preprocessor, a tool that transforms code before compilation. The syntax for most preprocessing directives is:

The command that adds external files to your program is called #include, and this is the command we will use the most for now.

Standard files are attached using angle brackets < >, but you can also create your own files and connect them to your project similarly, using double quotes " ".

How #include works

Look at the code below. One of the brackets is missing. Try to run this code and see what happens.

You get an error of a missing }. This is done on purpose to show how the #include works. We can create a separate file containing only the } symbol and include it in the main.cpp file using the #include directive.

The issue has been resolved, and you should no longer encounter an error. The reason for this resolution lies in the nature of the #include directive, which essentially just copies and pastes the content of a file at the point where it is called.