Elements of user defined functions: In order to make use of a user-defined function, we need to establish three elements that are related to functions.
The function definition is an independent program module that is specially written to implement to the requirements of the function.
In order to use the function we need to invoke it at a required place in the program. This is known as the function call.
The program or a function that has called a function is referred to as the calling function or calling program. The calling program should declare any function that is to be used later in the program. This is known as the function declaration.