num2str(x) - this converts the number to a string
Once converted subtracting '0' subtracts the character code for 0 from all entries. Therefore all zero characters become the actual value of 0, and all one characters become the actual value of 1 (since the ASCII code for '1' is one greater than the ASCII code for '0'). Subtracting 48 (the ascii code for '0' achieves the same thing).
>> '0' - 48
>> '1' -48