C Integer Constants
An "integer constant" is a decimal (base 10), octal (base 8), or hexadecimal (base 16) number that represents an integral value. Use integer constants to represent integer values that cannot be changed.
Integer constants are positive unless they are preceded by a minus sign (–). The minus sign is interpreted as the unary arithmetic negation operator. (See Unary Arithmetic Operators for information about this operator.)
If an integer constant begins with 0x or 0X, it is hexadecimal. If it begins with the digit 0, it is octal. Otherwise, it is assumed to be decimal.
The following lines are equivalent:
0x1C /* = Hexadecimal representation for decimal 28 */ 034 /* = Octal representation for decimal 28 */
No white-space characters can separate the digits of an integer constant. These examples show valid decimal, octal, and hexadecimal constants.
/* Decimal Constants */ 10 132 32179 /* Octal Constants */ 012 0204 076663 /* Hexadecimal Constants */ 0xa or 0xA 0x84 0x7dB3 or 0X7DB3