FUNCTION CPU

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D E V I N B A B A R I Y A ( 3 3 )
U T K A R S H D U B E Y ( 3 4 )
K R U S H A L K A K A D I Y A ( 3 5 )
M E E T S O N I ( 3 7 )
P R I Y A M B H A T T ( 3 8 )
M I L A N S U T H A R ( 3 9 )
Subject: FUNCTION

INTRODUCTION
Every ‘C’ program is collection of functions. In every
‘C’ program, main() function must be there, because
the execution of program starts from main()
function.
Function is a group of statements as a single unit
known by some name which is performing some well
defined task.
The functions which are created by programmer in a
program are called as a user-defined functions.
The functions which are readily available in library
are called as library functions.

Advantages of Functions
 It facilitates top-down modular programming,
whereby the large problem is divided into small parts
and each small part is handled later in depth.
 Function can be used in other program also, so labor
is reduced.
 It reduced the size of code, if that code is repetitively
used in program.
 It allows term-work for large project, individual
members of term has to concentrate on function
given to them and not on whole complex problem.

User defined functions
 User defined functions are created for doing some
specific task in a program. The code is written as one
unit having a name.
 As the size of program increases, It becomes difficult
to understand.
 The code of function is written only once in the
program and called for any number of times from the
program whenever required.

Built-in functions
 These are the functions which are readily available
and placed in side the library.
 Their prototypes are declared in various header files
depending on the category to which they belong to.
 We need to understand the prototype of built-in
function and include that header file in our program.

Function declaration
 The syntax for declaring function is:
type function_name(argument(s));
Here, type specifies the type of value returned,
function_name specifies name of user defined
function, and in bracket argument(s) specifies the
arguments supplied to the function as comma
separated list of variables.
The declaration of a function is terminated by
semicolon (;) symbol. The declaration is also called
as prototype of a function.

Function Definition
 The syntax for definition of function is:
type function_name(argument(s));
{
statement(s);
}
Here, type, function_name and argument(s) have same meaning as
before. The statement(s) within { } symbols indicate the body of a
function. Here, the actual logic of the work of function is implemented.
If the return type is not mentioned, then by default it is taken as int. We
can not define function inside a function. We can call one function from
other. If the function return type is other than void, there must be return
statement in the function. The returned value can be put in brackets but it
is not compulsory.

Category of functions
 The function in ‘C’ language can be divided in following categories:
1) Functions with no arguments and no return value
2) Functions with arguments and no return value
3) Functions with arguments and with return value
When we have function which takes arguments, in that case we need to
understand the formal parameters and actual parameters.
The variables or parameters used in definition of function are called as
formal parameters. while, parameters used in the call to the functions are
called as actual parameters.

Scope of variables
 By scope of variables, we mean in what part of the
program the variable is accessible. There are two
types of scope.
1.) local and 2.) Global
Difference between local and global variables :
Local variables Global variables
Declared inside function body Declared outside body
Not initialized automatically Initialized automatic by value 0
Use of local variables advisable Too much use of global variables
make program difficult to debug, so
use with care

Parameter passing to function
 When a function is called from other function,the
parameters can be passed in two ways.
1) Call by value 2) Call by reference
1) Call by value : In call by value, argument value are
passed to the function , the contents of actual parameters
are copied into the formal parameters. The called function can not
change the values of the variables which are passed.
2) Call by reference : In call by reference, as the name suggests,
the reference of the parameter is passed to the function and not the
value. Call by reference is used whenever we want to change the
value of local variables declared in one function to be changed by
other function

Recursion
 Sometimes, the function is defined in terms of itself.
Recursion is the process by which a function calls itself.
Because the function calls itself , there must be some
condition to stop recursion; otherwise it will lead to infinite
loop.
Types of recursion:
Direct recursion :- In the case of direct recursion, a function explicitly
calls.
Indirect recursion :- The function calls another function, which ultimately
calls the caller function.
Advantages of recursion :
 Easy solution for recursively defined problems.
 Complex programs can be easily written in less code.

Parameters as array and string
As a array
 We can pass the whole array as a parameter to the function.
If we pass the name of an array as an argument, we are
effectively passing whole array as an argument. Naturally,
passing an address of an array is call by reference.
As a string
 It is character array as parameter, because string is stored
in a single dimensional array of character type. We can
write user defined functions to manipulate strings. In this
section , we will understand how a string can be passed as a
parameter to a function.

Storage classes
 The storage class of a variable determines the scope
and lifetime of a variable. There are four storage
classes.
1)Auto
2)Register
3)Static
4)External

Auto
If we do not specify the storage specify with variable,
by default it is auto. All the local variable have auto
storage class. Auto variables are stored in memory,
garbage initial value, scope local to function and
lifetime till the control remains in that function. As the
name suggests, auto variables are created when the
function is called and destroyed automatically when
the function terminates.

Register
Variables which are to be stored in the registers of CPU
are called as register variables. Register keyword is
used for that purpose, for example,
register int a;
declaration the variables as a register variable.
Storage of register variable take place in registers ,
have garbage value, scope local to function and are
created when the function is called and destroyed
automatically when the function terminates.

Static
All the global variables are by default of static storage
class. Default value of static variable is 0. static global
variable is available throughout the entire file in which
it is declared, while static local variable is available in
the function in which it is defined, but is initialized
only once and retains its value even when the control
goes out of the function.
Static variables are stored in memory, default initial
value 0, scope is local to function or file in which
declared and lifetime is entire program execution with
retaining values between function calls.

External
 Normally, the scope of global variable starts from its
definition up to the end of the program. So, the
functions which are defined before the definition of
global variable can not access it.
 Storage in memory, default initial value 0, scope is
global all the files of program and life is entire
program execution.

FUNCTION CPU

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