C Program to find sum of digits of a given number

//Program to find sum of digits of a given number
#include<stdio.h>
int main()
    {
    int a,r,num,sum=0;
    printf("\n enter a number:");
    scanf("%d",&a);
    if(a<0)
         num=-a;
    else
         num=a;
    while(num>0)
             {
        r=num%10;
        sum=sum+r;
        num=num/10;
         }
    if(a<0)   
          printf("\n sum of digits= -%d \n",sum);
    else
          printf("\n sum of digits=%d \n",sum);
return 0;
   }