May be I shouldn't declare "ExpressionContrs" as bytes?
That's right.
As the variables ExpressionContr are trying to hold a 14 bit number then bytes will not be big enough. While the value variables can be bytes ( a byte is 8 bits ) when you combine the two you need a type of variable with more bits. Use a int type variable, this will hold a maximum of 16 bits. The fact you only need 14 of them is not important because an int is the smallest variable type that will fit your number.