Integer Constants

Integer constants are numbers used directly in a sketch, like 123. By default, these numbers are treated as int's 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               Example    Formatter        Comment
 
10 (decimal)           123    none
 
2 (binary)        B1111011    leading 'B'      only works with 8 bit values (0 to 255)
                                               characters 0-1 valid
 
8 (octal)             0173    leading "0"      characters 0-7 valid       
 
16 (hexadecimal)      0x7B    leading "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.

Example:

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

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

Example:

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”

Example:

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 syted in upper or lower case (a-f).

Example:

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

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:

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

* constants * #define * byte * int * unsigned int * long * unsigned long

Source: arduino.cc