The popular C programming language is used for a huge range of applications, from the tiny microcontrollers used in toasters and watches up to complete operating systems. The first half of this book is an introduction to C, and covers the basics of writing simple command-line programs. The second half of the book shows how to use the GTK user interface toolkit with C to create feature-rich GUI applications which can be run on the desktop. No previous experience of C or GTK is required - even if you are an absolute beginner, this book will teach you all you need to know.In this book, you'll learn how to:Create simple command-line C programs.Control flow with conditions and loops.Handle variables, strings, and files.Design graphical user interface applications in C.Handle user input with buttons and menus.Use advanced UI features such as data stores and dialogs.Updated for GTK3, this book will teach you all you need to know to write simple programs in C and start creating GUIs. Although the examples in this book were developed on a Raspberry Pi running, Raspberry Pi OS, you can follow along on other operating systems, including Linux, macOS, and Windows with the Windows Subsystem for Linux.