What is Function oriented design?

Answer 1

Function oriented design breaks a system down into one or more named functions which transform their inputs to produce an output, such that the output of one function may be used as input to another function. In addition, the system also typically provides a global state which any function may operate upon.

In order for the "system of functions" to operate there has to be single point of entry which is typically provided by the system's global main function. The inputs for this particular function are derived from the command line used to invoke the system while the output is an integer typically used to indicate a system-defined error (with the value 0 usually indicating no error). Typically, the global main function decodes the command line parameters to determine what work is to be performed (if any) and to delegate that work to an appropriate function.

Although a single function can perform a significant amount of work, complex systems are much easier to understand when the work is divided amongst many smaller, simpler functions. When the functions are appropriately named, code becomes largely self-documenting, with the low-level implementation details largely hidden from the user.