An integer constant is a sequence of digits, with an optional prefix to denote its number base.

If the sequence of digits is preceded by 0x or 0X, then the constant is considered to be hexadecimal. Hexadecimal values may use the digits 0 to 9, and the letters a to f or A to F. The following are all valid hexadecimal constants: 0x1f 0x200 0x04A 0xbf0 0xDe0 0x8

If a sequence of digits is preceded by 0b or 0B, then the constant is considered to be binary. Binary values may use the digits 0 and 1. The following are all valid binary constants: 0b0110 0b11 0b11110

In any other case, the sequence of digits is assumed to be decimal. Decimal values may use the digits 0 to 9.