range aa=col(a); //Access column a on the active worksheet
range bb=col(b);
range cc=col(c);
range dd=col(d);

for( int ii = 1 ; ii <= aa.GetSize() ; ii++ )  //loop all rows
{
   if( aa[ii] < bb[ii] )
       cc[ii] = aa[ii]/bb[ii];
   else 
       dd[ii] = aa[ii]/bb[ii];
};