The numbers are in hexadecimal, so the correct format is 0x2A or 0x2a. All hexadecimal numbers are prefixed with 0x in C++, or # in some other languages.
This lets the compiler know the difference between a decimal '20' which means is 20 (we use decimal normally in english), and a hexadecimal '20' (0x20) which means 32 in decimal.