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A numeric character reference refers to a character by its Universal Character Set/Unicode code point, and a character entity reference refers to a character by a predefined name. A numeric character reference uses the format &#nnnn; or &#xhhhh; where nnnn is the code point in decimal form, and hhhh is the code point in hexadecimal form.
For example, \11 is an octal escape sequence denoting a byte with decimal value 9 (11 in octal). However, \1111 is the octal escape sequence \111 followed by the digit 1 . In order to denote the byte with numerical value 1, followed by the digit 1 , one could use "\1""1" , since C concatenates adjacent string literals.
The ASCII "escape" character (octal: \033, hexadecimal: \x1B, or, in decimal, 27, also represented by the sequences ^[or \e) is used in many output devices to start a series of characters called a control sequence or escape sequence. Typically, the escape character was sent first in such a sequence to alert the device that the following ...
Each of these number systems is a positional system, but while decimal weights are powers of 10, the octal weights are powers of 8 and the hexadecimal weights are powers of 16. To convert from hexadecimal or octal to decimal, for each digit one multiplies the value of the digit by the value of its position and then adds the results. For example:
Magic numbers become particularly confusing when the same number is used for different purposes in one section of code. It is easier to alter the value of the number, as it is not duplicated. Changing the value of a magic number is error-prone, because the same value is often used several times in different places within a program. [6]
PER Aligned: a fixed number of bits if the integer type has a finite range and the size of the range is less than 65536; a variable number of octets otherwise; OER: 1, 2, or 4 octets (either signed or unsigned) if the integer type has a finite range that fits in that number of octets; a variable number of octets otherwise
In C and C++, a leading zero indicates an octal value, e.g. 0755. This was primarily intended to be used with Unix modes; however, it has been criticized because normal integers may also lead with zero. [19] As such, Python, Ruby, Haskell, and OCaml prefix octal values with 0O or 0o, following the layout used by hexadecimal values.
Thus, the number of code units required to represent a code point depends on the encoding: UTF-8: code points map to a sequence of one, two, three or four code units. UTF-16: code units are twice as long as 8-bit code units. Therefore, any code point with a scalar value less than U+10000 is encoded with a single code unit.