Find sum of digits of a number using c++

#include<iostream.h>
#include<conio.h>
class s_digits{
 int num,sum;
public:
 void input();
 void calculate();
 void output();
};
void s_digits::input()
{
 cout<<"Enter your number:";
 cin>>num;
}
void s_digits::calculate()
{
 sum=0;
 int r,n;
 n=num;
 while(n>0)
 {
  r=n%10;
  sum+=r;
  n=n/10;
 }
}
void s_digits::output()
{
 cout<<"The number entered is:"<<num;
 cout<<"\nSum of its digits is:"<<sum;
}
void main()
{       clrscr();
 s_digits ob;
 ob.input();
 ob.calculate();
 ob.output();
 getch();
}