functIONS PROGRAMMING CIII II DJDJKASDJKJASD.pptx

Functions in c++
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Functions in C++
Functions are used to provide modularity to a
program. Creating an application using
function makes it easier to understand, edit,
check errors etc.
Functions allow to structure programs in
segments of code to perform individual tasks.
In C++, a function is a group of statements
that is given a name, and which can be
called from some point of the program.
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Functions in C++
Depending on whether a function is
predefined or created by programmer; there
are two types of function:
1. Library Function OR Built in function
2. User-defined Function
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Types
1.Built in functions :-
are part of compiler package.
Part of standard library made available by compiler.
Can be used in any program by including respective header file.
2. User defined functions:-
Created by user or programmer.
Created as per requirement of
the program.

User Defined Functions in C++
Syntax of Function
return-type function-name (parameters)
{
// function-body
}
return-type : suggests what the function will return. It can be int,
char, some pointer or even a class object. There can be functions
which does not return anything, they are mentioned with void.
Function Name : is the name of the function, using the function
name it is called.
Parameters : are variables to hold values of arguments passed
while function is called. A function may or may not contain
parameter list.
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09/25/202
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6 Parts of a function
main function
{
function prototype declaration
function call
-------;
}
function declaratory/definition
{
------;
return statement
}

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Function prototype
4 parts
i. Return type
ii. Function name
iii. Argument list
iv. Terminating semicolon
Variable declaration
Data_type variable_name ;
int x=5;
float marks;
int price;
A function prototype is a declaration of a function that tells
the program about the type of value returned by the
function, name of function, number and type of
arguments.
Syntax: Return_type function_name (parameter
list/argument);
EX: int add(int,int);
void add(void);
int add(float,int);

Declaring, Defining and Calling Function
#include < iostream>
using namespace std;
int sum (int x, int y); //declaring function
int main()
{
int a = 10;
int b = 20;
int c = sum (a, b); //calling function
cout << c;
}
int sum (int x, int y) //defining function
{
return (X + y);
}
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Function definition
Syntax: function_type function_name(parameter
list) {
Local variable
declaration; Function
body statement; Return
statement;
}
Function
body
2 parts
Function
header
Note: no semicolon in
header
Example: int add(int,int);
Z=add(x,y);
//prototype
//function call
//function definition
int add(int a,int b)
{
body statement;
Return(a+b);
P.P.Krishnara
}j RSET

P.P.Krishnaraj
RSET
Function
categories
i) Function with no return value and no argument.
void add(void);
ii) Function with arguments passed and no return value.
void add(int,int);
iii) Function with no arguments but returns a value.
int add(void);
iv) Function with arguments and returns a value.
int add(int,int);

I. Function with no return value and no argument
void main()
{
void disp(void);
//prototype //caller function
disp();
return 0;
}
void disp() //calle function
{
cout<<“--------”<<endl;
}
No arguments passed
from caller to calle
No value returned from
calle to caller function
P.P.Krishnaraj
RSET

P.P.Krishnaraj
RSET
//program to print square of a number using functions.
void main()
{
void sqr(void);
sqr();
getch();
return 0;
}
void
sqr()
{
int no;
cout<<“enter a no.”;
cin>>no;
cout<<“square
of”<<no<<“is”<<no
*no;
}

ii. Function will not return any value but passes argument
#include<iostream.h>
#include<conio.h>
void add(int,int);
int main()
{
int a,b;
cout<<“enter values of a and b”<<endl;
cin>>a>>b;
add(a,b);
getch();
return 0;
}
void
add(int
x,int y)
{
int c;
c=x+y;
cout<<
“additi
on
is”<<c
;
add(a,b);
a
b
void add(int x,int y);
P.P.Krishnaraj
RSET

iii) Function with arguments and return value
main function
{
int sqr(int);
int a,ans;
cout<<“enter a number”;
cin>>a;
ans=sqr(a);
cout<<“square of number is”<<ans;
getch();
return 0;
}
//function prototype
//function call
int sqr(int X)
{
return(X*X);
}
//function declaratory/definition
P.P.Krishnaraj
RSET

iv) Function with no arguments but returns a value
int main()
{
int add(void);
int z;
z=add();
cout<<sum
of 2 nos
is”<<z;
getch();
return 0;
}
int add(void);
{
int a,b;
cout<<“enter 2 nos”;
cin>>a>>b;
return(a+b);
}
Function call
add(x,y);
i.e z=add(x,y);
P.P.Krishnaraj
RSET

Calling a Function
Functions are called by their names. If the function is
without argument, it can be called directly using its
name. But for functions with arguments, we have two
ways to call them:
1. Call by Value
2. Call by Reference
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Call by value
A function can be invoked in two
manners (i)call by value
(ii)call by reference
The call by value method copies the value of actual parameters into
formal parameters i.e the function creates its own copy of
arguments and uses them.
add(a,b); Values of variables a
and b are passed to
X,Y
Now if you change
the value of X and Y
,
those changes are
not seen in a and b
Call by value
where the values of
variable are passed
to functions
}
void add(int x,int y);
{
--------;
P.P.Kris}hnaraj RSET

/* program to illustrate the concept of call
by value */
#include<iostream.h
#include<conio.h> void
add(int,int);
int main()
{
int a,b;
cout<<“enter values of a and b”<<endl;
cin>>a>>b;
add(a,b);
getch(); return 0;
}
void add(int x,int
y)
{
int c; c=x+y
cout<<“addition is”<<c;
}

Call by reference
In call by reference method in place of calling a value to the function being
called , a reference to the original variable is passed .i.e the same variable
value can be accessed by any of the two names.
add(a,b);
}
P.P.Krishnaraj
RSET
void add(int &x,int &y);
{
--------;
}
In function call
We write
reference variable
for formal
arguments
&X,&Y will be the
reference variable for
a and b. if we
change X and Y,
Value of a and b are
changed accordingly
No need for return
statement

Program to illustrate call by reference
#include<iostream.h>
#include<conio.h>
void swap(int &,int
&); int main()
{
int a,b;
cout<<“enter the values of a and
b”; cin>>a>>b;
cout<<“before
swaping”;
cout<<“A”<<a;
cout<<“B”<<b;
swap(a,b);
cout<<“after swaping”;
cout<<“A”<<a;
cout<<“B”<<b;
getch();
}
void swap(int &X,&Y)
{
int temp;
temp=X;
X=Y;
Y=X;
}
P.P.Krishnaraj RSET

Inline function
Calling a function generally causes a certain
overhead (stacking arguments, jumps,
etc...), and thus for very short functions, it
may be more efficient to simply insert the
code of the function where it is called,
instead of performing the process of formally
calling a function.
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Inline function
Preceding a function declaration with the
inline specifier informs the compiler that
inline expansion is preferred over the usual
function call mechanism for a specific
function.
This does not change at all the behavior of a
function, but is merely used to suggest the
compiler that the code generated by the
function body shall be inserted at each
point the function is called, instead of being
invoked with a regular function call.
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Inline function
C++ inline function is powerful concept that is
commonly used with classes. If a function is
inline, the compiler places a copy of the
code of that function at each point where
the function is called at compile time.
To inline a function, place the
keyword inline before the function name
and define the function before any calls are
made to the function.
The compiler can ignore the inline qualifier in
case defined function is more than a line.
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Inline function
Following is an example, which makes use of
inline function to return max of two numbers:
#include <iostream>
inline int Max(int x, int y)
{ return (x > y)? x : y; }
// Main function for the program
int main( ) {
cout << "Max (20,10): " << Max(20,10) << endl; cout <<
"Max (0,200): " << Max(0,200) << endl; cout << "Max
(100,1010): " << Max(100,1010) << endl; return 0;
}
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Friend function
A friend function of a class is defined outside
that class' scope but it has the right to
access all private and protected members
of the class. Even though the prototypes for
friend functions appear in the class
definition, friends are not member functions.
A friend can be a function, function template,
or member function, or a class or class
template, in which case the entire class and
all of its members are friends.
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Friend function
To declare a function as a friend of a class,
precede the function prototype in the class
definition with keyword friend as follows:
class Box {
double width;
public:
double length;
friend void printWidth( Box box );
void setWidth( double wid );
};
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Friend function
#include <iostream>
// forward declaration
class B;
class A
{
private:
int numA;
public:
A(): numA(12) { } // friend function declaration
friend int add(A, B);
};
class B {
private:
int numB;
public:
B(): numB(1) { } // friend function declaration
friend int add(A , B);
};
// Function add() is the friend function of classes A and B
// that accesses the member variables numA and numB
int add(A objectA, B objectB)
{
return (objectA.numA + objectB.numB);
}
int main()
{ A objectA;
B objectB;
cout<<"Sum: "<< add(objectA, objectB);
return 0;
}
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Friend function
In this program, classes A and B have
declared add() as a friend function.
Thus, this function can access private data of
both class.
Here, add() function adds the private data
numA and numB of two objects objectA and
objectB, and returns it to the main function.
To make this program work properly, a forward
declaration of a class class B should be made
as shown in the above example.
This is because class B is referenced within the
class A using code: friend int add(A , B);.
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Recursive function
A function that calls itself is known as recursive
function. And, this technique is known as
recursion.
void recurse()
{
... .. ...
recurse();
... .. ...
}
int main()
{
... .. ...
recurse();
... .. ...
}
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Examples of Recursive Function
// Factorial of n = 1*2*3*...*n
#include <iostream>
int factorial(int);
int main()
{
int n;
cout<<"Enter a number to find factorial: ";
cin >> n;
cout << "Factorial of " << n <<" = " << factorial(n);
return 0;
}
int factorial(int n)
{
if (n > 1)
{
return n*factorial(n-1);
}
else
{
return 1;
}
}
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