1. Why
User Defined Function is needed?
2.
Definition
3.
Function
in C Language
4.
Return
Values and their Types
5.
Arguments
and Return value combination.
6.
Scope
and lifetime of variables in functions
7.
Storage
Classes
8.
Nesting
of Functions
9.
Recursion
10. Functions and Arrays
11. Summary
1.
Why User Defined Function
is needed?
·
The large programs are divided into
functional parts, then each part may be coded independently and then combined
into a single unit.
·
Some type of operations are repeatedly
used throughout the program. Such part can be written as a function and called
whenever required .
·
It saves space and time also.
·
It reduces the length of the source program.
·
Top-down modular programming is done. i.e high
level logic of the problem is solved first then details of lower level function
solved.
2.
Definition
Function is a set of statements which perform particular task together.
3.
Function in C
Language
C functions are divided into two
categories
1.
Library
function
Library functions are predefined. They are
not needed to write by user.
e.g. scanf(),prinf,exit,
2.
User-defined
function
These are defined by user at the time of writing
program.
Syntax:
4.
Return Values and
their Types
5.
Arguments and Return
value combination.
6.
Scope and lifetime
of variables in functions
Definitions:
Scope
: It
is a parts of program where variable is available for use.
Lifetime:
It
is a period during which variable retains a given value during execution of
program.
Categories of variable:
1.
Local / Internal
variable
A variables which are declared within
particular function or block of the program.
2.
Global / external
variable
A variables
which are declared outside of any function.
7.
Nesting of Functions
Nesting of function call is allowed in C Language.
e.g main function calls Function1(),Function1
calls Function2 and which in turns call another function such type of nesting
is allowed
*Note: One cannot write function definition within another function
definition
Another
example:
function1(a, function2(p) );
8.
Recursion:
Definition:
A
Function which calls itself is known as recursion.
e.g
int Factorial(int n)
{
1.
if(n==1)
2.
return
1;
3.
else
4.
return(n*factorial(n-1));
}
Let us see detail execution
of the recursion
In above function ,
n=5;
Now value 1 is returned from factorial(1)
function call is put into the previous function factorial(2) who calls
factorial(1) and so on….
Let us see the sequence
of execution .
Whole sequence of execution is as follows:
Red color -indicates statements are executed.
Blue color -indicates statements are in execution phase but not completed due to recursive call.
Black solid arrow-show the transfer of control because of recursive call.
Red dotted arrow-shows returning of control after recursive function call finishes.
9.
Functions and Arrays
How to pass array to a
function?
In
Calling function: Pass an array name without subscript and
size of an array
e.g maximum(a,n);
Where a
is an array name and n is the size of array.
In
Function Definition:
Sample
Program:
10. Summary
·
Function
is used to modularize the program.
·
Function
can return only one value.
·
Function
may or may not return a value.
·
Function
return integer value by default.
·
Actual
and formal parameter must be same in data type.
·
Function
with return value must return some value with specified data type.
·
Function
can have more than one return statements.
·
A
Return statement can be written anywhere within function.
·
A
function can be written before or after main function.
·
Function
can not be defined inside another function.
·
A
variable declared inside function is local to that function .It is destroyed
when function is exited.
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