Integer Constants

[Constants]

描述

Integer constants are numbers that are used directly in a sketch, like 123. By default, these numbers are treated as int but you can change this with the U and L modifiers (see below).

Normally, integer constants are treated as base 10 (decimal) integers, but special notation (formatters) may be used to enter numbers in other bases.

Base範例Formatter評論
10 (decimal)123
2 (binary)B1111011leading ‘B’only works with 8 bit values (0 to 255)
characters 0-1 valid
8 (octal)0173leading ‘0’characters 0-7 valid
16 (hexadecimal)0x7Bleading “0x”characters 0-9, A-F, a-f valid

Decimal is base 10. This is the common-sense math with which you are acquainted. Constants without other prefixes are assumed to be in decimal format.

101 // same as 101 decimal ((1 * 10^2) + (0 * 10^1) + 1)

Binary is base two. Only characters 0 and 1 are valid.

B101 // same as 5 decimal ((1 * 2^2) + (0 * 2^1) + 1)

The binary formatter only works on bytes (8 bits) between 0 (B0) and 255 (B11111111). If it is convenient to input an int (16 bits) in binary form you can do it a two-step procedure such as:

myInt = (B11001100 * 256) + B10101010; // B11001100 is the high byte

Octal is base eight. Only characters 0 through 7 are valid. Octal values are indicated by the prefix “0”.

0101 // same as 65 decimal ((1 * 8^2) + (0 * 8^1) + 1)

*Warning:
It is possible to generate a hard-to-find bug by (unintentionally) including a leading zero before a constant and having the compiler unintentionally interpret your constant as octal.

Hexadecimal (or hex) is base sixteen. Valid characters are 0 through 9 and letters A through F; A has the value 10, B is 11, up to F, which is 15. Hex values are indicated by the prefix “0x”. Note that A-F may be typed in upper or lower case (a-f).

0x101 // same as 257 decimal ((1 * 16^2) + (0 * 16^1) + 1)

U & L formatters

By default, an integer constant is treated as an int with the attendant limitations in values. To specify an integer constant with another data type, follow it with:

  • 'u' or 'U' to force the constant into an unsigned data format. Example: 33u
  • 'l' or 'L' to force the constant into a long data format. Example: 100000L
  • 'ul' or 'UL' to force the constant into an unsigned long constant. Example: 32767ul

參考


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