Before you can work in the CDT, you must create a project to store your source code, makefiles, binaries, and related files. C/C++ projects are displayed in the C/C++ Projects view.
Tip: Nested projects are not supported. Each project must be organized as a discrete entity. Project dependencies are supported by allowing a project to reference other projects that reside in your workspace. For more information, see Selecting referenced projects.
For more information about projects and where they are stored, see:
You can create a C or C++ project.
To build your project, you can either create your own makefile, or let CDT generate the makefiles for you automatically.
You can toggle these modes (generate makefiles or not) at any time for existing project. Use properties.
You can convert projects from C to C++ (or from C++ to C). If, for example, your requirements change and you must convert an existing C project to C++, you can do this without recreating the project. The CDT converts your project files and resolves any source control issues.
For more information about projects, see Workbench User Guide > Concepts > Workbench > Resources.
Project file views
How to bring C/C++ source into Eclipse
Working with C/C++ project files
Converting a C or C++ nature for a project