[redhead]

You're off by one:

      for (i=0; i < a_elem; i++)   {
           printf("\nelement: ");
           scanf("%d ", &i_array[index]);
           index++;           
        }
     index=a_elem;

When exiting this loop your index is pointing at the NULL terminating your initial array.
So when you reverse:

     
     for (i=0; i< a_elem; i++)     {
           rev_array[rev_index]=i_array[index];
           index--;
           rev_index++;             
        }

Your initial value will be an int representing NULL as the first value in the reversed array. And since you're testing i against the array size, you'll miss the first value in your initial array.