C/C++ Program to find sum of digits of a given number

//Program to find sum of digits of a given number
#include<iostream>
using namespace std;
int main()
{
int a,r,num,sum=0;
cout<<"\n enter a number:";
cin>>a;
if(a<0)
    num=-a;
else
    num=a;
while(num>0)
{
    r=num%10;
    sum=sum+r;
    num=num/10;
}
if(a<0)   
    cout<<"\n sum of digits= -"<<sum<<endl;
else
    cout<<"\n sum of digits="<<sum<<endl;
return 0;
}