What is the basic unit of a C language program?

The basic unit of a C language program is a function. A C language program consists of multiple functions, with one being the main function, which is called and executed first when the program runs. Other functions can be called and executed by the main function or by other functions. Each function has a function header and a function body, with the function header specifying the return type, function name, and parameter list, while the function body contains the actual implementation code. Functions can pass data and combine functionality through function calls.