Question

In java, c or c++ code, when a number begins with a leading 0, what do you know about that number: (example: int zzz = 012;) in java, c or c++ code, when a number begins with a leading 0x, what do you know about that number: (example: int zzz =0x12;) in java, c or c++ code, when a number begins without a prefix, what do you know about that number: (example: int zzz =12;)

Answer 1

A leading 0 denotes octal notation, so the digits 8 and 9 are not used.
In normal decimal notation 12 means 1*10+2, in octal, it means 1*8+2.

The leading 0x denotes hexadecimal notation, here the digits are extended with 6 letters, a through f. 0x12 means 1*16+2.

Without any prefix, we have normal decimal notation.