Integer constants, that is, integer constants, have three representations in C language:

Decimal notation: for example, 123, -345.

Octal notation: Start with the number 0, such as 0 12 (this is an octal number).

Hexadecimal notation: starting from 0x, such as 0x 123 (hexadecimal number).

The default data type of integer constants is int type, that is, signed integer type.