The representation of decimal integer constants is the same as that in mathematics. Decimal integer constants consist of numbers from 0 to 9 without prefix.
2. Octal integer constant
The expression of octal integer constant begins with the number 0, which is the prefix of octal number and consists of numbers from 0 to 7.
3. Hexadecimal integer constant
The expression of hexadecimal integer constant is prefixed with 0X or 0x and consists of numbers 0~9, letters A~F or a ~ f.