User Defined Functions:



In some situations, while designing complex programs, a user may require performing some specific task repeatedly and there is no library function available for performing the task. Hence to solve this problem, the programmer writes his own function(s) as per requirements in the program. These functions which are defined specifically by the user to meet his requirements are called user-defined functions.
In order to make use of a user-defined function, we need to establish three elements that are related to functions.
1.      Function definition.
2.      Function call.
3.      Function declaration

The function definition is an independent program module that is specially written to implement the requirements of the function. In order to use this 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 calls the function is referred to as the calling program or calling function. The calling program should declare any function (like declaration of a variable) that is to be used later in the program. This is known as the function declaration or function prototype.

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