User defined Function

USER-DEFINED FUNCTIONS

What is function? When it is used?

· When the program become very large and complex and as a result the task of debugging, testing and maintaining become difficult.

· Than a program is divided in to small parts then each part may be independently code and letter combine in to a single unit, this sub program called function.

· Function is much easier to understand, debug and test the program.

· When certain types of operation or calculation use repeated at many points through of program so this save both time and space.

· A function is a self contain block of code that perform a particular task.

Syntax:

return-type functionrf-name (argument-list)

{

//function body

}

Example:

void print _line(void):

main ():

{

print _line():

printf("stop:):

}

void print _line (void)

{

for int, i = o:i<g:i++)

Printf ("this is a computer"):

}

· The program execution begins with the main function.

· During execution of the main the first statement in counter is, print_ line():

1. At this point the program control is transfer to the function print _ line.

2. After execute the print _ line function , the control is transfer back to the main

3. Any function can call any other function.

4. Function can call itself.

5. A function can be called more then once.

6. A call function can be place either before or after the calling the function..

Advantages of function

· The length of a source program can be reducing by using function at appropriate place.

· It is easy to locate and isolate a faulty function for further investigation.

· A function may be use by many other programs.

· Function gives facilities top down modular programming.

Elements of function

Three elements of function are:

1. Function definition :

2. Function call

3. Function declaration

· A function definition is also known as function implementation.

· The program that call the function is refer to as the calling function.

· Function declaration is also known as function prototyping.

What is function prototyping

· A function declaration is known as the function prototyping.

· Function proto type concise of four parts.

a) Function type (return type)

b) Function name

c) Parameter use

d) Terminating semicolon.

· Syntax:

Function_type function_name(parameter list);

· Example:

int mul (int m, int n)

· A prototype declaration may be place in two places in a program

1. Above all the function

2. Inside function definition

· When we place the declaration above all the function the prototype is called global prototype.

· When we place it in a function definition the prototype is called a local prototype.

Difference between actual arguments and formal arguments.

Actual arguments	formal arguments
actual arguments are the source of information;	formal arguments are not the source of information;
The calling programs pass actual arguments to called functions.	The called functions access the information using corresponding formal arguments.
actual arguments belong to the calling function.	Formal arguments belong to the called function.
A change in actual arguments would be reflected in the formal arguments.	A change in formal arguments would not be reflected in the actual arguments.
Actual arguments are not a copy of the formal arguments.	Formal arguments are a copy of the actual arguments.

Difference between function prototype and function definition.

Function prototype	Function definition
The declaration, called the function prototype, tells the computer the name, return type and parameters of the function.	The function definition tells the compiler what task the function will be perfoming
It has terminating semicolon	It has no terminating semicolon
The function prototype consists of the function	The function definition consists of the function.
Syntax Return type functionname(arguments)	Syntax Returntype functionname(arguments)

Difference between call by value and call by deference.

Call by value	Call by reference.
In call by value mechanism we have to pass the variable as the argument to the function.	In call by reference mechanism we have to pass the reference of the variable as the argument to the function.
Syntax: return-type function-name (data-type variable-name) { . . . . . //function body}	Syntax: Return-type function-name (data-type & variable-name) { . . . . . //function body}
In call by value, if the value of the variable is change then it does not reflect to the original value of the variable.	In call by reference, if the value of the variable is change then it does reflect to the original value of the variable.
It creates the new set of variable for the function.	It does not create the new set of variable but the reference of the variable for the function.
Program occupies more memory if the call by value mechanism is used.	Program occupies less memory then the program uses the call by mechanism if the call by reference is used.