calling by reference and call by value C function to swap two given numbers reference mechanism

(a)  What is calling by reference? How it is different from call by value?

Write a C function to swap two given numbers using call by

reference mechanism. 

If you are calling by reference it means that compilator will not create a local copy of the variable which you are referencing to. It will get access to the memory where the variable saved. When you are doing any operations with a referenced variable you can change the value of the variable.

                Call by value is where a copy of an object is placed in the parameter stack. The called function can access and manipulate that copy at will, but it cannot change the original copy because it has no way of knowing where that original copy is located. Call by Reference, on the other hand, is where the address of an object is placed in the parameter stack. Using extra syntax, the * or the ->, the called function can access and manipulate the original copy at will.

                #include<stdio.h>

                #include<conio.h>

                void swap(int *num1, int *num2);

                void main()

                {

                                clrscr();

                                int x,y;

                                printf(“Enter the number: “);

                                scanf(“%d”,&x);

                                printf(“Enter the number: “);

                                scanf(“%d”,&y);

                               printf(“x= %d y= %d \n”,x,y);

        swap(&x,&y);

                                printf(“x= %d y= %d”,x,y);

                                getch();

                }

                void swap(int *num1, int *num2)

                {

                                int temp;

                                temp=*num1;

                                *num1=*num2;

                                *num2=temp;

                }