Working modulus 11

Enter the digits of the ISBN code, one per line.
Use a ? to mark the number which is missing...
A line with just a . will end this program

The ISBN code entered is: 0 5 5 ? 1 0 2 0 6 10 

Sum before modulus = 198
Sum after modulus = 0
Value of missing element, including coefficient = 0
Coefficient of missing element = 4
Multiplicative inverse of this coefficient = 3
Unknown element = 0