c-Functions power point presentation on c functions

Introduction
What is function?
How functions will work?
How to declare a function in C language?
What are the different types of functions are
there in C language?
Example programs.

Modular Programming
Modular Programming
Break a large problem into smaller pieces
Smaller pieces sometimes called ‘modules’ or
‘subroutines’ or ‘procedures’ or functions
Divide and Conquer
Divide and Conquer

Why Modular Programming?
Why Modular Programming?
Helps in managing the complexity of the
program
- Smaller blocks of code - Easier to read
Encourages re-use of code
Within a particular program or across different programs
Allows independent development of code
Provides a layer of ‘abstraction’

What is function?
Function is a set of instructions to carry out a particular task.
The Function after processing returns a single value.
In other word, we say a Function is a group of statements
that can perform any particular task.
Function in programming is a segment that groups a number
of program statements to perform specific task

Every C program has at least one function, which is main().
We have already used functions like…..

Every function in C must have two things…
A function declaration tells the compiler about a function's
name, return type, and parameters.
A function definition provides the actual body of the
function.

A function declaration tells the compiler about a function's
name, return type, and parameters.
A function declaration must be done within main function or
before main function.

A function definition must be done before main function or
after main function.
A function definition provides the actual body of the
function.

Types of functions?
Predefined
Userdefined

Predefined functions
Actually all predefined functions in C Language are defined
inside in any one of the header files.
If the functionality of a function is defined by the compiler
those functions are called predefined functions.
The functionality of the predefined function is fixed, users
cannot change or redefine it.

Predefined functions
Predefined functions are also called as System Defined
functions or Library functions.
NOTE

User-defined functions
User-defined functions are small programs that you can
write to perform an operation.
If the functionality of a function is defined by the user those
functions are called user-defined functions.
Users are free to define their own code for the user-defined
functions. Every user-defined function must have the
following….

Declaring User-defined functions
Syntax
Example
We also call it as Function Prototype
NOTE

Definition of User-defined functions
Syntax
Example

Calling User-defined functions
Syntax
Example

Example Program
void main()
{
int a, b, c;
void addition(int , int);
printf(“We are in main…..n”);
printf(“Enter any two numbers: ”);
scanf(“%d%d”, &a, &b);
addition(a, b);
printf(“We are again in main…..”);
}
void addition(int x, int y)
{
printf(“SUM = %dn”, x+y);
}

Important terms in functions
It is nothing but a function declaration
It is used to initiate the function execution. That means this
line decides when a function has to be perform its task.
It is nothing but the function definition. It decides what is to
be done by the function on a function call.

Example Program
void main()
{
int a, b, c;
void addition(int , int);
printf(“We are in main…..n”);
printf(“Enter any two numbers: ”);
addition(a, b);
printf(“We are again in main…..”);
}
void addition(int x, int y)
{
printf(“SUM = %dn”, x+y);
}
Prototype
Calling
Called

Parameters & Return Value
Parameters are the data values which are passed from
calling function to called function
Return value is the data value which passed from called
function to calling function
For a function we can have any number of parameters
For a function we can have only one return value
In a function the total number of parameters and the order
of the parameters must be same in all function prototype,
function calling and function definition

Parameters & Return Value
To return a value from called function to calling function we
use ‘return’ statement

Parameter types
In C programming language there are two types of
parameters

These are the parameters used at the time of function
calling
Whenever we pass actual parameters copy of its value is
sent to the called function but not entire variable

These are the parameters used at called function as
receivers of the actual parameters
The order of the actual parameters and their datatypes
should exactly match with the order and datatypes of the
formal parameters

Function types
Based on the parameters and return value, functions are
classified into FOUR types

In this type, there is no data transfer between calling and
called functions
Simple control transfer from calling function to called
function, executes called function body and comes back to
the calling function.
Everything is performed within the called function like
reading data, processing data and displaying result.
This type of functions are used to print some message,
line….

void main()
{
void add();
printf(“We are in main….n”);
add();
printf(“We are again in main….n”);
}
void add()
{
int a,b,c;
printf(Enter any two numbers: );
c = a + b;
printf(“Result = %d”, c);
}

void main( )
{
void add( );
add( );
}
void add( )
{
int a,b,c;
c = a + b;
}
Control
No input
Control
No return value

In this type, there is data transfer from calling to called
function, but not from called to calling function.
function along with some data (parameters), executes called
function body and comes back to the calling function
without any data.
This type of functions are depend on the calling function.
Generated result is utilized by called function and nothing
will be sent back to the calling function.

void main()
{
void add( int, int );
add( 10, 20);
}
void add(int a, int b)
{
int c;
c = a + b;
}

void main( )
{
void add( int, int );
add( 10, 20 );
}
void add( int a, int b)
{
int c;
c = a + b;
}
Control
10 & 20 as input
Control
No return value

In this type, there is no data transfer from calling to called
function, but from called to calling function one data is sent.
function, executes called function body and a data value is
sent back to the calling function from called function.
This type of functions are called function is independent. It
reads data, process data and result is sent back to the calling
function.

void main()
{
int c;
int add( );
c = add( );
printf(“Result = %dn”, c);
}
int add( )
{
int a, b;
printf(“Enter any two numbers:”);
return (a + b);
}

void main( )
{
int c;
int add( );
c = add( );
}
void add( )
{
int a,b;
return (a + b);
}
Control
No input
Control
30 as return value
input values for a & b are 10 & 20 respectively

In this type, there is data transfer from calling to called
function, and from called to calling function one data is sent
back.
Control transfer from calling function to called function
along with data, executes called function body and a data
value is sent back to the calling function from called
function.
In this type of functions are called & calling functions both
dependent on each other.

void main()
{
int c;
int add( int, int );
c = add( 10, 20 );
}
int add( int a, int b)
{
return (a + b);
}

void main( )
{
int c;
int add( int, int );
c = add( 10, 20 );
}
void add( int a, int b)
{
return (a + b);
}
Control
10 & 20 as input
Control
30 as return value

Different ways to make a function call
There are THREE ways of making function call…

1.
1. From main function
From main function
We have already seen making a function call from main
function.
When we make a function call from main, the control
transfers to called function, executes it, again comes back to
the main function.

2. From another user-defined function
2. From another user-defined function
We can also make a function call from another user-defined
function.

void main()
{
function1();
}
void function1()
{
function2();
}
void function2()
{
body of the function;
}

3. From same function
3. From same function
We can also make a function call from same function. That
means function calls itself
If a function calls itself, then it is called as “RECURSION”.
When a function calls itself until the last call is invoked till
that time the first call also remains open.
At every time, a function invoked, the function returns the
result of previous call.

void main( )
{
printf(“This is example of Recursion!!!”);
main( );
}
This is example of Recursion!!!
…….

int factorial( int );
void main( )
{
int fact, n;
printf(“Enter any positive integer: ”);
scanf(“%d”, &n);
fact = factorial( n );
printf(“Factorial of %d is %d”, n, fact);
}
int factorial( int n )
{
int temp;
if( n == o)
return 1;
else
temp = n * factorial( n-1 );
return temp;
}

int factorial( int );
void main( )
{
int fact, n;
printf(“Enter any positive integer:
”);
scanf(“%d”, &n);
fact = factorial( n );
printf(“Factorial of %d is %d”, n,
fact);
}
{
int temp;
if( n == o)
return 1;
else
return temp;
}

{
int temp;
if( n == o)
return 1;
else
return temp;
}
n = 3 n
3
temp
{
int temp;
if( n == o)
return 1;
else
return temp;
}
3 * factorial(2)
n = 2
n
2
temp
{
int temp;
if( n == o)
return 1;
else
return temp;
}
2 * factorial(1)
n = 1
{
int temp;
if( n == o)
return 1;
else
1 * factorial(0)
n
1
0
n
temp
temp
n = 0
1
1
1
1*1 = 1
2
2*1 = 2
2
3*2 = 6
6
6
Memory Allocation

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