Functions in C

INTRODUCTION TO FUNCTIONS
TYPES OF FUNCTIONS
ELEMENTS OF USER DEFINED FUNCTIONS
TYPES ON THE BASIS OF ARGUMENTS AND
RETURN VALUES
METHODS OF CALLING A FUNCTION
Functions

Introduction to Function
Block of statements that perform the particular task.
Enables modular programming.
Main() is the driver function.
Has pre defined prototype.
Same function can be accessed from different places
within a program.
Once a function execution is completed , control
return to the place from where the function was
called.

Advantages
Modular Programming
Length of source program can be reduced
Easy to locate and isolate faulty function
Functions can be used by other program’s

Types of Functions
Library (Built In) Functions:
 They are written in the header files.
 To use them appropriate header files should be included.
Header Files Functions Defined
stdio.h Printf(), scanf(), getchar(), putchar(),
gets(), puts(), fopen(), fclose()
conio.h Clrscr(), getch()
Ctype.h Toupper(), tolower(), isalpha()
Math.h Pow(), sqrt(), cos(), log()
Stdlib.h Rand(), exit()
String.h Strlen(), strcpy(), strupr()

User Defined Functions
 Written by the user at the time of programming.

Elements of User defined functions
Function Prototype
Function Call
Function arguments and parameters
Function Definitions

Function prototype
It specify the type of value that is to be return from
the function and that is to be passed to the function.
It is defined in the beginning before the function call
is made.
Syntax:
 return-type name-of-function(list of arguments);
 Example
Void sum(int, int);

Function Call
A function can be called by specifying name and list
of arguments enclosed in parenthesis and separated
by comma.
If there is no arguments empty parenthesis are place
after function name.
If function return a value, function call is written as
assignment statement as:
 A=sum(x,y);

Function arguments and parameters
Arguments are also called actual parameters.
Arguments are written within parenthesis at the time
of function call.
Parameters are also called formal parameters.
These are written within parenthesis at the time of
function definition.

Function Definition
It is the independent program module.
It is written to specify the particular task that is to be
performed by the function.
The first line of the function is called function
declarator and rest line inside { } is called function
body

Return statement
It is the last statement of the function that return
certain values.
It return certain types of values to the place from
where the function was invoked.
Syntax:
 return(variable-name or constant);

Categories of function
Function with no arguments and no return
Function with arguments but no return
Function with no arguments and return
Function with arguments and return

Function with no argument and no return

Function with argument and no return

Function with no argument and return

Function with argument and return

Methods of calling function
Call by value
Call by reference

Call by value
Copies the value of actual parameters into formal
parameters.
During execution whatever changes are made in the
formal parameters are not reflected back in the
actual parameters.

Call by Reference
Reference(address) of the original variable is passed.
Function does not create its own copy, it refers to the
original values by reference.
Functions works with the original data and changes
are made in the original data.

Functions in C

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