Reference

Call by value
Call by address
Call by reference

Call by value

Example 1:

// call by value
#include <iostream>
using namespace std;

void fun(int num)
{
    num = num + 2;
    cout<<"Inside function "<<num<<endl;
}
int main() {

    int num = 10,
    cout<<"Before function :"<<num<<endl;

   fun(num);
    cout<<"After function :"<<num<<endl;

    return 0;
}

Output :

Before function : 10
Inside function : 12
After function : 10

Expalantion

create function fun pass parameter num.
calculate num = num + 2.
print Inside function and num.
In main function initialize num variable and store 10 value.
print Before function and num.
call fun funaction pass argument num.
print After function and num.

Call by address

Example 2:

//call by address
#include <iostream>
using namespace std;


void fun(int *num)
{
    *num = *num + 2;

    cout<<"Inside function :"<<*num<<endl;
}
int main() {

    int num = 10
    cout<<"Before function :"<<num<<endl;
    fun(&num);
    cout<<"After function "<<num<<endl;

    return 0;
}

Output :

Before function : 10
Inside function : 12
After function : 10

Expalantion

create function fun pass parameter *num.
calculate *num = *num + 2.
print Inside function and *num.
In main function initialize num variable and store 10 value.
print Before function and &num.
call fun funaction pass argument num.
print After function and num.

Call by reference

Example 3:

//call by reference
#include <iostream>
using namespace std;

int main() {

    int a = 10;
    int& b = a;
    cout<<a<<endl;
    cout<<b;

    return 0;
}

Output :

10
10

Expalantion

Initialise a variable and store 10 value.
Initialise b variable and store refrence of a.
print a endl for new line.
print b.