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What is function???? Function is a self contained block of statements that

perform a coherent task of some kind.

Every C program can be a thought of the collection offunctions.

main( ) is also a function.

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Types of Functions.

Library functions

These are the in- -built functions of C library.

These are already defined in header files. e.g. printf( ); is a function which is used to print at

output. It is defined in stdio.h file .

User defined functions.

Programmer can create their own function in C toperform specific task

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Why use functions?Writing functions avoids rewriting of the same code

again and again in the program.

Using function large programs can be reduced tosmaller ones. It is easy to debug and find out the errorsin it.

Using a function it becomes easier to write program to

keep track of what they are doing.

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Function Declarationret_type func_name(data_type par1,data_type par2);

Function Definationret_type func_name(data_type par1,data_type par2)

{

}

Function Call

func_name(data_type par1,data_type par2);

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Function prototypeA prototype statement helps the compiler to check the

return type and arguments type of the function.

A prototype function consist of the functions returntype, name and argument list.

Example

int sum( int x, int y);

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Example#include#include

void main(){clrscr();

void print(); /*func declarationprint(); /*func callingprintf(no parameter and no return value);print();getch();}

void print() /*func defination{

For(int i=1;i

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#include

void main(){clrscr();int a=10,b=20;int sum(int,int);

int c=sum(a,b); /*actual argumentsCout

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Function parameters The parameters are local variables inside the body of

the function.

When the function is called they will have the valuespassed in.

The function gets a copy of the values passed in (we willlater see how to pass a reference to a variable).

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Arguments/Parametersone-to-one correspondence between the

arguments in a function call and the

parameters in the function definition.int argument1;double argument2;// function call (in another function, such as main)result = thefunctionname(argument1, argument2);

// function definitionint thefunctionname(int parameter1, double parameter2){// Now the function can use the two parameters// parameter1 = argument 1, parameter2 = argument2

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a) Actual arguments:-the arguments of calling functionare actual arguments.

b) Formal arguments:-arguments of called function areformal arguments.

c) Argument list:-means variable name enclosed withinthe paranthesis.they must be separated by comma

d) Return value:-it is the outcome of the function. theresult obtained by the function is sent back to thecalling function through the return statement.

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Return statement It is used to return the value to the calling function.

It can be used in fallowing ways

a) return(expression) return(a+b);b) A function may use one or more return statement

depending upon condition

if(a>b)

return(a);else

return(b);

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c) return(&a); returns the address of the variable

d)returns(*p);returns value of variable through the

pointere)return(sqrt(r));

f)return(float (sqrt(2.4)));

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Categories of functions

A function without parameter and return value

A function without parameter and no return value

A function with parameter and return value

A function with parameter and no return value

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A function with no parameter and no return value#include

void main()

{clrscr();

void print(); /*func declarationprint(); /*func callingCout

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A function with no parameter and no return value

There is no data transfer between calling and calledfunction

The function is only executed and nothing is obtained Such functions may be used to print some messages,

draw stars etc

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A function with parameter and no return value

#include

void main(){

clrscr();

int a=10,b=20;

void mul(int,int);

mul(a,b); /*actual arguments

getch();

}

void mul(int x, int y) /*formal arguments

{int s;

s=x*y;

Cout

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A function with parameter and return value#include

void main()

{clrscr();

int a=10,b=20,c;

int max(int,int);

c=max(a,b);

Cout

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A function without parameter and return value#include

void main()

{

clrscr();

int a=10,b=20;int sum();

int c=sum(); /*actual arguments

Cout

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Argument passing techniques

Pass By Value

Pass By Reference Pass By Pointer\address

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Call By Value It is a default mechanism for argument passing.

When an argument is passed by value then the copy ofargument is made know as formal arguments which isstored at separate memory location

Any changes made in the formal argument are notreflected back to actual argument, rather they remain

local to the block which are lost once the control isreturned back to calling program

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Examplevoid main()

{

int a=10,b=20;void swap(int,int);

Cout

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void swap(int x,int y)

{

int z;z=x;

x=y;

y=z;

Cout

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Output:

before function calling a=10 b=20

value of x=20 and y= 10after function calling a=10 b=20

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Call By pointer/address In this instead of passing value, address are passed.

Here formal arguments are pointers to the actualarguments

Hence change made in the argument are permanent.

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Example

Void main()

{

int a=10 ,b=25;void swap(int *,int *);

Cout

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void swap(int *x,int *y)

{

int z;z=*x;

*x=*y;

*y=z;

Cout

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Output:

before function calling a= 10 b= 25value of x=25 and y=10

after function calling a=25 b= 10

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Using Reference Variables

with Functions To create a second name for a variable in a

program, you can generate an alias, or an

alternate name

In C++ a variable that acts as an alias for another

variable is called a reference variable, or simply areference

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Declaring Reference Variables You declare a reference variable by placing a type and

an ampersand in front of a variable name, as indouble &cash; and assigning another variable of the

same type to the reference variabledouble someMoney;

double &cash = someMoney;

A reference variable refers to the same memoryaddress as does a variable, and a pointer holds thememory address of a variable

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Pass By Reference

void main()

{

int i=10;int &j=i; // j is a reference variable of I

cout

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Output:-Value 10 10

modified value 20 20

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#includevoid swap(int &iNum1, int &iNum2);

void main(){int iVar1, iVar2;cout

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Declaring Reference Variables There are two differences between reference

variables and pointers: Pointers are more flexible

Reference variables are easier to use

You assign a value to a pointer by inserting anampersand in front of the name of the variablewhose address you want to store in the pointer

It shows that when you want to use the value storedin the pointer, you must use the asterisk todereference the pointer, or use the value to which itpoints, instead of the address it holds

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Comparing Pointers and

References in a Function Header

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Passing Variable Addresses to Reference

Variables

Reference variables are easier to use because you dontneed any extra punctuation to output their values

You declare a reference variable by placing anampersand in front of the variables name

You assign a value to a reference variable by usinganother variables name

The advantage to using reference variables lies increating them in function headers

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Passing Arrays to Functions An array name actually represents a memory address

Thus, an array name is a pointer

The subscript used to access an element of an arrayindicates how much to add to the starting address tolocate a value

When you pass an array to a function, you are actually

passing an address

Any changes made to the array within the functionalso affect the original array

examp e

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examp e#include

void main()

{void printarr(int [ ]);int a[5];printf(enter the elements of array);for(int i = 0;i

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Inline Functions Each time you call a function in a C++ program, the

computer must do the following:

Remember where to return when the function eventually ends

Provide memory for the functions variables

Provide memory for any value returned by the function

Pass control to the function

Pass control back to the calling program

This extra activity constitutes the overhead, or cost ofdoing business, involved in calling a function

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Using an Inline Function

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Inline Functions

An inline function is a small function with no callingoverhead

Overhead is avoided because program control never

transfers to the function A copy of the function statements is placed directly

into the compiled calling program

The inline function appears prior to the main(),

which calls it Any inline function must precede any function that

calls it, which eliminates the need for prototyping inthe calling function

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Inline Functions

When you compile a program, the code for the inlinefunction is placed directly within the main() function

You should use an inline function only in thefollowing situations:

When you want to group statements together so that you canuse a function name

When the number of statements is small (one or two lines inthe body of the function)

When the function is called on few occasions

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Using Default Arguments

When you dont provide enough arguments in a functioncall, you usually want the compiler to issue a warningmessage for this error

Sometimes it is useful to create a function that supplies a

default value for any missing parameters

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Using Default Arguments

Two rules apply to default parameters:

If you assign a default value to any variable in a function prototypesparameter list, then all parameters to the right of that variable also

must have default values If you omit any argument when you call a function that has default

parameters, then you also must leave out all arguments to the rightof that argument

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Examples of Legal and Illegal

Use of Functions with Default Parameters

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Recursion

When function call itself repeatedly ,until somespecified condition is met then this process is calledrecursion.

It is useful for writing repetitive problems where eachaction is stated in terms of previous result.

The need of recursion arises if logic of the problem is

such that the solution of the problem depends uponthe repetition of certain set of statements withdifferent input values an with a condition.

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Two basic requirements for recursion :

1. The function must call itself again and again.2. It must have an exit condition.

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Factorial using recursion

void main()

{

clrscr();

int rect(int);

int n,fact;Coutn;

fact=rect(n);

Cout

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int rect(int a)

{

int b;

if(a==1)

{

return(1);

}

else

{

b=a*rect(a-1);

return(b);

}

}

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Stack representation

Rec(3)Rec(3)

3*Rec(2)

Rec(3)3*Rec(2)

3*2*Rec(1).

.

Rec(3)

3*Rec(2)

3*2*Rec(1)

3*2*1

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Advantages of recursion1. It make program code compact which is easier towrite and understand.

2. It is used with the data structures such aslinklist,stack,queues etc.

3. It is useful if a solution to a problem is in repetitiveform.

4. The compact code in a recursion simplifies thecompilation as less number of lines need to be

compiled.

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Disadvantages

1. Consume more storage space as recursion calls andautomatic variables are stored in a stack.

2. It is less efficient in comparison to normal programin case of speed and execution time

3. Special care need to be taken for stopping conditionin a recursion function

4. If the recursion calls are not checked ,the computermay run out of memory.

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Pointer to Function Function pointers are pointers, i.e. variables, whichpoint to the address of a function.

The syntax to declare to declare a function pointer is as

follows:[return_type] (*pointer_name)[(list_of_parameters)]

example:

Function declaration int add(int ,int);

Pointer declaration int(*ptr)(int,int);Assigning address of the function to pointer

ptr=add;

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Example#include

#include

Void main()

{

clrscr();int x=3,y=5,z;

int add(int , int);

int (*ptr)(int,int);

ptr=add;z=(*ptr)(x,y);

Cout

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Contd

int add(int x,int y)

{

return(x+y);

}

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Polymorphism

The word polymorphism is derived from Greek wordPoly which means many and morphos which means

forms.

Polymorphism can be defined as the ability to use thesame name for two or more related but technicallydifferent tasks.

Eg-woman plays role of daughter,sister,wife,motheretc.

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Overloading in C++What is overloading

Overloading means assigning multiple

meanings to a function name or operator

symbol

It allows multiple definitions of a function with thesame name, but different signatures.

C++ supports Function overloading

Operator overloading

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Why is Overloading Useful? Function overloading allows functions thatconceptually perform the same task on

objects of different types to be given the

same name.

Operator overloading provides a convenient

notation for manipulating user-defined

objects with conventional operators.

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Function Overloading

Is the process of using the same name for two or morefunctions

Requires each redefinition of a function to use adifferent function signature that is:

different types of parameters,

or sequence of parameters, or number of parameters

Is used so that a programmer does not have toremember multiple function names

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Function Overloading Two or more functions can have the same name but

different parameters

Example:int max(int a, int b){

if (a>= b)return a;

elsereturn b;

}

float max(float a, float b){

if (a>= b)return a;

elsereturn b;

}

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Overloading Function Call

Resolution Overloaded function call resolution is done by

compiler during compilation

The function signature determines which definition

is used

a Function signature consists of:

Parameter types and number of parameters

supplied to a function a Function return type is not part of function signature

and is not used in function call resolution

E l

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ExampleVoid sum(int,int);

Void sum(double,double);Void sum(char,char);

Void main()

{

int a=10,b=20 ;

double c=7.52,d=8.14;

char e=a , f=b ;

sum(a,b);sum(c,d);

sum(e,f);

}

C d

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Contd..Void sum(int x,int y)

{Cout

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Output:

Sum of integers 30

sum of two floating no are 15.66

sum of characters are 195

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