Two numbers are input through the keyboard into two locations C and D. Write a program in C to interchange the contents C and D

Two numbers are input through the keyboard into two locations C and D. Write a program in C to interchange the contents C and D. 

            #include <stdio.h>
            #include <conio.h>
            void main() {
                        int a=10, b=15;
                        clrscr();
                        printf("Old sequence: ");
                        printf("\na = %d \nb = %d", a, b);
                        a=a+b;
                        b=a-b;
                        a=a-b;
                        printf("\n\nNew sequence: ");
                        printf("\na = %d \nb = %d", a, b);
                        getch();
            }