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Call by Reference

                  In call by reference technique, reference or memory address of the variables are passed to a
                  function. In this technique, changes made to the parameters inside the function are reflected on
                  the arguments.
                  Program 4: To swap two numbers by using call by reference method of function call.

                  #include<iostream.h>
                  #include<conio.h>
                  void swap(int *num1, int *num2);
                  void main(){
                      int a = 10, b = 20;
                      clrscr();
                      cout<<”The values before swapping are: “<<a<<” and “<<b<<”\n”;
                      swap(&a, &b);
                      cout<<”The values of and b are: “<<a<<” and “<<b<<”\n”;
                      getch();
                  }                                                                   Output:
                  void swap(int *num1, int *num2){                                    The  values  before  swapping  are:
                        int temp;                                                     10 and 20
                        temp = *num1;                                                 The values after swapping are: 20
                                                                                      and 10
                        *num1 = *num2;
                                                                                      The values of and b are: 20 and 10
                        *num2 = temp;
                        cout<<”The values after swapping are: “<<*num1<<” and “<<*num2 <<”\n”;
                  }
                  In the preceding program, the references of the parameters are passed to the function by using
                  the address operator (&) as:

                  swap(&a, &b);
                  You need to pass the formal arguments to the function with the help of dereference operator (*) as:
                  swap(int *num1, int *num2)

                      SCOPE OF VARIABLES

                  The scope of a variable means how the different parts of the program can access that variable.
                  There are two main types of scopes for variables in C++: local and global.
                  Local Variables


                  The variables which are declared in the body of a function or block are called local variables for
                  that function. You can use these variables only inside the function in which they are declared. If
                  you try to use the local variables outside their scope, C++ compiler will show an error message.
                  Global Variables

                  The variables that are declared outside of all the functions are called global variables. Global
                  variables can be used by any function in the program. Generally, global variables are declared
                  just below the preprocessor directive.


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