Parameter(argument) Passing Techniques

Introduction Parameter passing is a mechanism for communication of data and

information between the caller and callee It can be achieved either by passing the value or address of the variable C++ supports the following three types of parameter passing techniques Pass by Value Pass by Address Pass by Reference The parameters can be classified as formal and actual parameters

Pass by value It does not change the contents of argument variable in the caller, even if they are changed in the callee, because the contents of the actual parameter in a caller is copied to the formal parameter in the callee The function parameter is stored in the local data area of the callee Changes to the parameter within the function will affect only the copy and

will have no effect on the actual arguments

Demonstrates parameter passing by value

#include<iostream.h>void swap(int x, int y){ int temp; cout<<“Before swapping in

swap():”<<x<<y<<endl; temp=x; y=temp;cout<<“After swapping in

swap():”<<x<<y<<endl;}

main( ){ int a=1, b=2; swap(a, b); cout<<“After swapping in

main() :”<<a<<b<<endl; //values remain unaltered}OutputBefore swapping in swap(): 1 2After swapping in swap() : 2 1After swapping in main() : 1 2

Pass by value is not suitable in situation When a large class object must be passed as an argument. The time and space

costs to allocate and copy the class object on to stack When the values of the arguments must be modified

Pass by address C++ provides another means of passing values to a function known as Pass

by address Instead of passing the value, the address of the variable is passed In the function, the address of the argument is copied into a memory location

instead of the value The dereferencing operator is used to access the variable in the called

function

//Demonstrates parameter passing by pass by address

#include<iostream.h>void swap( int *x, int *y){ int temp;cout<<“Before

swapping:”<<a<<b<<endl;temp=*x;*x=*y;*y=temp;return;}

main( ){ int a=1, b=2; swap( &a, &b);cout<<“After swapping in main():

“<<a<<b<<endl; // value altered}OutputBefore swapping :1 2After swapping : 2 1After swapping in main(): 2 1

Pass by Reference The function call is similar to that of call-by value In the function declarator , those parameters, which are to be received must

be preceded by & operator The reference type formal parameters are accessed in the same way as

normal value parameters

Note :1. A reference can never be null, it must always refer to a legal object2. Once established, a reference can never be changed so as to make it point to

a different object3. A reference does not require any explicit mechanism to dereference the

memory address and access the actual data value

//Demonstrates argument passing by pass by reference

#include <iostream.h>void swap(int &x, int &y){ int temp:cout<<“Before

swapping:”<<a<<b<,endl;temp=x;x=y;y=temp;return ;}

main ( ){ int a=1, b=2; swap(a, b); cout<<“After swapping in main() :

“<<a<<b<<endl; //value altered}

Uses and advantages of declaring a parameter as a reference

1. Function receives the lvalues of the argument rather than a copy of its value2. Returns additional results to the calling function3. Pass large class objects to a function

Passing objects as arguments Objects can be passed as parameter to a function either by pass by value or

by reference Other objects can be passed as arguments to function and the result is not

returned by the function Result is automatically stored in the object of which the function is a

member

//demonstrates passing objects as parameter to a function

#include<iostream.h>class Dist{ int feet; float inch; public: Dist() { } Dist(int x, float y) {feet=x;inch=y;} void show() {cout<<feet<<“\’-”<<endl;void add_dist(Dist d, Dist d2){ inch=d1.inch+d2.inch; feet=0; if (inch >=12.0) { inch=inch-12.0; feet++; } feet=feet+d1.feet+d2.feet;}};

main( ){ Dist dist1(17, 5.75), dist2(11, 6.25); Dist dist3; dist3.add_dist(dist1, dist2);cout<<“Distance1:”<<dist1.show();cout<<“Distance2:”<<dist2.show();cout<<“Distance3:”<<dist3.show();}

Output:Distance 1: 17’-5.75’’Distance 2 : 11’-6.25”Distance 3:29’-0”

Recursion Recursion is a technique of defining something in terms of itself In the field of mathematics and computer science, many concepts can be

explained using recursion In computer terminology, if a function calls itself then it is known as

recursive function If the function calls itself directly, then it is known as Direct recursionExample : void myfun() { ---------- ---------- myfun(); ----------- }

Continues…. If the function calls itself through another function, then it is known as indirect

recursion

Example : void myfun() { ----- fun(); ------ } void fun() { ------ myfun(); ---------- }Note : the function myfun() is calling the function fun(), which in turn calls myfun(). Such

a recursive call is know as indirect recursive

//Factorial of a number#include<iostream.h>long fact(int);void main( ){ int n;cout<<“Enter the value of n”; cin>>n;if (n<0)cout<<“Invalid input”;elsecout<<“\n Factorial of “<<n<<“is”<<n<<fact(n);}

long fact(int n){ if (n== 0) return 1;else return n*fact(n-1); }

Continues…. some facts recursive function Recursive functions do not usually reduce the code size They do not improve memory utilization compared to iterative function Many of the recursive functions may execute a bit slower compared to

iterative functions because of the overhead of repeated function calls They may cause a stack overrun, as each new call to the recursive function

creates a new copy of variables and parameters and puts them into the stack Advantage Recursion function is to create clearer and simpler programs

//Demonstrates function #include<iostream.h>void swap(char &x, char &y){ char t; t=x; x=y; y=t;}void swap(int & x, int &y){ int t; t=x; x=y; y=t;} void swap(float &x, float &y){ float t; t=x; x=y; y=t;}

main(){ char ch1, ch2;cout<<“Enter two characters\n”;cin>>ch1>>ch2;swap(ch1,ch2);cout<<“On swapping (ch1,ch2):”<<ch1<<“ “<<ch2<<endl;int c1, c2;cout<<“Enter two characters\n”;cin>>ch1>>ch2;swap(c1,c2);cout<<“On swapping (c1,c2):”<<c1<<“ “<<c2<<endl;float f1, f2;cout<<“Enter two characters\n”;cin>>f1>>cf2;swap(f1,f2);cout<<“On swapping (f1,f2):”<<f1<<“ “<<f2<<endl;}There may be several functions which needs to be used frequently with different data types. The limitation of such function is that, they operate only on a particular data type

Function Templates

Introduction Template is one of the features added to C++ recently New concept which enable us to define generic classes and functions Provides support for generic programmingGeneric Programming : An approach where generic types are used as parameters in algorithms , it work for a variety of suitable data types and data Structures A template can be used to create a family of classes or functions A template can be considered as a kind of macro A template is defined with a parameter that would be replaced by a specified data type at the time of actual use of the class or function The templates are sometimes called parameterized classes or functions

Continues..General format of a function templatetemplate<class T>returntype functionname (arguments of type T){ //……. //Body of function //with type T //wherever appropriate}