2. Parameter defination.
Types of parameter.
Call by value.
Call by Reference.
Advantages of call by reference.
Disadvantages of call by reference.
.

3. PARAMETERS
 A parameter is an intrinsic property of the procedure,
included in its definition.
 Parameter passing methods are the ways in which
parameters are transferred between functions when
one function calls another.
 C++ provides two parameter passing methods--pass-
by-value and pass-by-reference .

4. Types of parameter
 Parameters are of two types
 Formal parameters
 Actual parameters

5. Formal parameters
 Formal parameters are written in the function
prototype and function header of the definition.
 Formal parameters are local variables which are
assigned values from the arguments when the function
is called.

6. Value Parameter Rules
 Formal parameter is created on function invocation and it is initialized
with the value of the actual parameter.
 Changes to formal parameter do not affect actual parameter.
 Reference to a formal parameter produces the value for it in the
current activation record.
 Formal parameter name is only known within its function.
 Formal parameter ceases to exist when the function completes.

7. Example of Formal Parameters
Return type Function name Formal parameter
float CircleArea (float r) {
const float Pi = 3.1415;
Local object
Definition return Pi * r * r;
}
 Return statement Function body


8. Actual Parameters
 When a function is called, the values (expressions) that
are passed in the call are called the arguments or actual
parameters (both terms mean the same thing).
 The time of the call each actual parameter is assigned to
the corresponding formal parameter in the function
definition.

9. Example of Actual Parameter
Actual parameter
cout << CircleArea(MyRadius) << endl
To process the invocation, the function that contains the
insertion statement is suspended and CircleArea()
does its job. The insertion statement is then completed
using the value supplied by CircleArea().

10. A function can be invoked in 2
ways
Call by value
Call by Reference

11. Call By Value
 The call by value method copies the values of actual
parameter in formal parameter.
 That is the function create its own copy of argument
value and then uses it.

12. Example of call by value
#include<iostream.h>
int main( )
{ int cube(int); Formal Parameter
int vol,side=7; 7
: a
vol=cube(side);
: value copied
cout<<vol;
7
Return 0; side
} Actual parameter
int cube(int a)
{ return a*a*a*;
}

13. Call By Reference
 In call by reference method the called function does
not create its own copy rather it refers to original value
only by different name i.e reference.
 When function is called by reference then ,the formal
parameter become reference or alias to the actual
parameter in calling function.

14. Example of Call By Reference
#include <iostream.h>
void duplicate (int& a, int& b, int& c)
{ a*=2; b*=2; c*=2;
}
int main ( )
{
int x=1, y=3, z=7;
duplicate (x, y, z);
cout << "x=" << x << ", y=" << y << ", z=" << z;
return 0;
}
x=2, y=6, z=14

15. Advantages of passing by
reference:
 It allows us to have the function change the value of
the argument, which is sometimes useful.
 Because a copy of the argument is not made, it is fast,
even when used with large structs or classes.
 We can pass by const reference to avoid unintentional
changes.
 We can return multiple values from a function

16. Disadvantages of passing by
reference
 It can be hard to tell whether a parameter passed by
reference is meant to be input, output, or both.
 An argument passed by value and passed by reference
looks the same. We can only tell whether an argument is
passed by value or reference by looking at the function
declaration. This can lead to situations where the
programmer does not realize a function will change the
value of the argument.
 Because references are typically implemented by C++ using
pointers, and dereferencing a pointer is slower than
accessing it directly, accessing values passed by reference is
slower than accessing values passed by value.