adding even position and substracting odd position of a number

#include<stdio.h>
void main()
{
int a=275,b=153,x[3],y[3],c[3],r,n,i=2,j=2;
clrscr();
do
{
r=a%10;
x[i]=r;
a=a/10;
i--;
}while(a>0);

do
{
n=b%10;
y[j]=n;
b=b/10;
j--;
}while(b>0);

//printf("%d%d%d\n",x[0],x[1],x[2]);
//printf("%d%d%d\n",y[0],y[1],y[2]);
for(i=0;i<3;i++)
{ if(i%2==0)
  c[i]=x[i]+y[i];
  else
  c[i]=x[i]-y[i];
  }
//printf("\n%d%d%d",c[0],c[1],c[2]);
n=0,i=0;
n=n+c[i];
do
{
i++;
n=n*10;
n=n+c[i];
}while(i<2);
printf("%d",n);
}

OUT PUT:
328