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1 integer
There are two integer encoding: one can only represent non-negative number (a number greater than 0), another can represent negative, zero, and positive.
(1) integer data type:
C and C ++ support signed (the default) and unsigned, Java support only a signed number.
(2) unsigned code:
Unsigned binary representation of another very important attribute:
Each between 0 ~ 2 ^ w - has a unique number between 1 and a value of w bits coding, and vice versa.
(3) complement encoding:
The most common have signed a computer representation that complement (two's-complement) form: most-significant-bit word as a negative right (negative weight), which is the sign bit.
Like an unsigned representation, each number within the range can be represented by a unique complement of the bit coded w - Uniqueness of complement encoding.
There are two attention to detail:
A) the scope of complement is asymmetric: | TMin | = | Tmax | + 1, i.e. TMin no corresponding positive - negative number indicates a general pattern of bits (the sign bit is a number), the other. half represents a non-negative number, and 0 is non-negative, it can be represented by a positive number less than negative one.
b) maximum unsigned value than 2 times the maximum value just complement large 1: UMax = 2TMax + 1.
- there is a point Note: maximum UMax -1 complement and unsigned bit representation of the same - through a full 1, while a value of 0 in both string representation are all zero.
C language standard does not require the use complement form to represent a signed integer, but almost all of the machines are doing.
So for portability program, developers do not manually change represents a range of values, and do not assume that signed will use other special representation.
- Extended: disassembler is an executable program file is converted back to a more readable ASCII codes of these files contain many hexadecimal numbers, all with typical complement form to represent these values .
can recognize numbers generated by the disassembler and understand their meaning, is an important skill.
(4) with a converter between the number and the unsigned number notation:
C language allows casts made between various types of digital data.
Achieve the most C language, the process has the same word length general rule conversion between symbols and unsigned numbers: The numbers may change, the value stored in the bit pattern does not become low level .
Signed and unsigned numbers (5) C language
Most digital by default is signed, to create an unsigned number, you must add the suffix character 'U' or 'u', for example: 12345U, or 0x1A2Bu.
C language, as with
printfthe output value, respectively, with the indicator%对,%uand%xrepresents a signed decimal, unsigned decimal and hexadecimal form a digit.
To be continued ...