Type of User defined functions, No argument no return, With argument no return, With argument with return, Prototype of a function, Function Definition, Accessing a function, Parameter Passing, Call by value, Call by reference, Recursion

Type of User defined functions:-

          The user defined functions may be classified in the following three types. Each type is based on the formal arguments or parameters passed to the functions and the usage of return statement.

No argument no return:-

          A function is called without passing any argument from the calling portion of a program and also the function does not return any value to the calling function.

With argument no return:-

          A function is called and formal arguments are passed from the calling program but function does not return any value to the calling program.

With argument with return:-

          A function is invoked with formal arguments form the calling portion of a program and the function return value to the calling program.

Prototype of a function:-

          The prototype tells ‘C’ compiler in advance about some characteristics of a function used in a program.

          Syntax:-

                             type   function_name(type_argument1,type_argument2,……..);

          The function “type” is the type of the returned value. If the function does not return a value, the function name is any legal identifier followed by the parenthesis.

          The arguments or parameters are given inside the parenthesis, preceded by their type and separated by commas.

Function Definition:-

          A function definition contains the code that will be executed when a function is called upon.

          Syntax:-

                         return_type   function_name(type_argument1,type_argument2,….);

                         {

                                      statement;

                                      statement;

                          }

Accessing a function:-

          A user defined function is called from the main program simply by using the name of the function, including the parenthesis followed by a semicolon.

Parameter Passing:-

          Parameter passing is a method for communication of data between the calling function and called function. This can be done by following two type-

• Call by value
• Call by reference

Call by value:-

          In C, arguments are passed by the value, which means that a copy of the argument is passed to function. The function can change the value of this copy but cannot change the value of the argument is calling function.

          Note:-

                   The argument that is passed is often called an actual argument and while the received copy is called a formal argument or formal parameter.

Call by reference:-

          Call by reference technique passes the addresses or references of the actual parameter to the called function. Thus the actual and formal parameters share the some memory locations. This is achieved by applying an address operator, that is the ‘&’ to the formal parameters in the function definition.

Recursion:-

          A Recursion function is a function that calls itself to perform a specific operation. The process of a function calling itself is known as recursion.