How to use Function Parameters in C++

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FUNCTION PARAMETERS IN C++

This tutorial provides function parameters in c++, call by reference in c++, call by value and call by reference in c++, reference argument in c++ with clear examples.

PARAMETERS

It is the essential part of function. However, it is optional but it makes C++ function more dynamic than simple function
It is used to passing information or value to a function and then function calculate the value and then returns appropriate results
Based on type of parameters, a function responses and returns value
C++ supports two types of method parameters. They are:

Call by value (Pass by value)
Call by reference (Pass by reference)

1. CALL BY VALUE (PASS BY VALUE)

In call by value, original data is not modified
By default, function arguments are passed by value in C++
The value of actual parameter is copied to formal parameter (Sending a variable to the function through value)
If there are any changes in formal parameters that do not reflect the value of actual parameters. Because both parameters are allocated in different memory addresses.

Actual Parameter (Actual Arguments)

A parameter in calling function (function calling) or function declaration is called actual parameter.

Formal Parameter (Dummy Arguments)

A parameter called function (function definition) is called formal parameter or dummy parameter.

NOTE

It creates separate memory locations for both actual and formal parameters.

I. EXAMPLE OF CALL BY VALUE

1. SOURCE CODE

#include <iostream>

using namespace std;

void change(int d)

{

d+=10;

cout<<“Inside the method\n”;

cout<<“Value of formal parameter : “<<d<<endl;

cout<<“————————————-\n”;

}

int main()

{

cout<<“————————————-\n”;

cout<<“\tCall by Value\n”;

cout<<“————————————-\n”;

int a=30;

cout<<“Before passing value to function\n”;

cout<<“Value of actual parameter : “<<a<<endl;

cout<<“————————————-\n”;

// call by value

change(a);

cout<<“After passing value to function\n”;

cout<<“Value of actual parameter : “<<a<<endl;

cout<<“————————————-\n”;

return 0;

}

2. OUTPUT

2. CALL BY REFERENCE

Here, the address of the actual parameter is copied to formal parameter (Sending a variable to the function through address)
The changes in the formal parameter should reflect the actual parameter. Because both are using same memory address space
In c++, the “call by reference” is implemented with help of pointer and reference “&” modifier.

CONDITIONS

Only variables are allowed
Expressions, Constants are not allowed.

Example

swap(& (a+b), x) // wrong, because of expression
swap(&45); // wrong because of constant

POINTS

Unlike call by value, it does not create a new storage location (memory address), instead it just shares the memory address of formal parameter (dummy argument)

IMPLEMENTATIONS

In c++, the call by address is implemented using two ways. They are:

1. Through Pointers (Pointer variable)

2. Through Reference (Reference variable)

II. CALL BY ADDRESS USING POINTERS

1. SOURCE CODE

#include <iostream>

using namespace std;

void change(int *ptr)

{

*ptr+=10;

cout<<“Inside the method\n”;

cout<<“Value of formal parameter : “<<*ptr<<endl;

cout<<“————————————-\n”;

}

int main()

{

cout<<“————————————-\n”;

cout<<“\tCall by Reference\n”;

cout<<“————————————-\n”;

int a=25;

cout<<“Before passing value to function\n”;

cout<<“Value of actual parameter : “<<a<<endl;

cout<<“————————————-\n”;

// call by reference

change(&a);

cout<<“After passing value to function\n”;

cout<<“Value of actual parameter : “<<a<<endl;

cout<<“————————————-\n”;

return 0;

}

2. OUTPUT

EXPLANATION (REFERENCE PARAMETER)

REFERENCE VARIABLE

Unlike c language, c++ provides new features called as reference variable
Like pointer, it is used to access and manipulate memory
It is an alias (alternate name to existing variable)
Unlike a pointer, it must be initialized with the value / refer of some variable. Because it cannot be NULL.
A reference variable is similar to a pointer. In many cases, this variable is used as an alternative to pointer.

Working Operation

A reference works as a pointer.
A reference is declared as an alias of a variable.
It stores the address of the variable.

Syntax

Example

EXAMPLE OF REFERENCE VARIABLE

SOURCE CODE

#include<iostream>

using namespace std;

int main()

{

int f=95; // Normal local variable

int &r=f; // Reference variable

cout<<“\tReference Variable\n”;

cout<<“————————————–\n”;

cout<<“Variable =”<<f<<endl;

cout<<“Reference Variable =”<<r<<endl;

cout<<“————————————–\n”;

r=60;

cout<<“Variable =”<<f<<endl;

cout<<“Reference Variable =”<<r<<endl;

cout<<“————————————–\n”;

f=90;

cout<<“Variable =”<<f<<endl;

cout<<“Reference Variable =”<<r<<endl;

cout<<“————————————–\n”;

return 55;

}

OUTPUT

CALL BY ADDRESS USING REFERENCE VARIABLE

Aim of this code is used to implement the concept of call by address using a reference variable.

SOURCE CODE

#include <iostream>

using namespace std;

void change(int &rf) // reference variable

{

rf=rf+15;

cout<<“Inside the method\n”;

cout<<“Value of formal parameter : “<<rf<<endl;

cout<<“——————————————\n”;

}

int main()

{

cout<<“—————————————\n”;

cout<<“\tCall by Reference-Via Reference\n”;

cout<<“—————————————\n”;

int a=25; // actual variable

cout<<“Before passing value to function\n”;

cout<<“Value of actual parameter : “<<a<<endl;

cout<<“—————————————\n”;

change(a);

cout<<“After passing value to function\n”;

cout<<“Value of actual parameter : “<<a<<endl;

cout<<“—————————————\n”;

return 0;

}

OUTPUT

DIFFERENCE BETWEEN CALL BY VALUE & CALL BY REFERENCE

S.N	CALL BY VALUE	CALL BY REFERENCE
1.	Copy of the value is passed to the function (Arguments are passed via value)	Copy of the address is passed to function (Arguments are passed by address)
2.	Original value is not modified	Original value is modified
3.	The actual and formal parameters are using different memory locations	Actual and formal parameters are using the same memory location.

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