Basic data type

    constant : Data is immutable during operation

    variable : Data can be changed during operation

    identifier : Such as type name , Variable name , Function name

    1, integer

         long           4 byte         Range : Unsigned 0-2 Of 32 Power -1    Signed -2 Of 31 Power   - 
2 Of 31 Power -1

         short          2 byte    

         int             Usually 4 Bytes , But different platform lengths are different  

    

         signed       Signed      Represents the highest order when the symbol is used

         unsigned   Unsigned       Represents the highest bit when the number is used

        

         constant : 234  Default to integer ( instead of char or short This needs attention )

                    234L  long type ( Long integer )

                    234U Unsigned int type

                    234UL  Unsigned long type

         Base :

                    Binary     In coding   Unable to express directly    
supplement :0b101010110 Not expressible in code , A lot of people don't pay attention to this

                    decimal system     123

                    octal number system     0123               0 As a distinction

                   hexadecimal 0x123              0x As a distinction

         Base conversion : Decimal to other base use 10 Base number divided by base , Remainder is the converted number , Quotient continued division , And then there's the remainder to go forward , Until Shang Wei 0 stop
                          Other decimal to decimal Multiply the base number with the preceding bit , Add with the following bits , It's going to be the last decimal , Until the end of the last bit calculation
  

         example :

                  ? Which of the following numbers are long
                   721387821387983  0L  0xFFFFFFFFFFF
01234234252341324               
                   0L It's long , All others default int
       
                   ? Which of the following constants are written correctly
                   2341234  0x9fkw8sw 032913  0432
                   032913 Octal medium , Meet 8 Enter one , So it's impossible to include 8 Number above
                   0x9fkw8sw Octal medium , Meet 16 Enter one , So it's impossible to include 16 Number above

         Signed and unsigned memory structures :

                   All data structures are stored in computer by complement

                   Codebook : Able to represent data 2 Base

                   Inverse code : Original code 2 Negation of base number

                   Complement : On the basis of inverse code +1

                   example :  7                  0b0000 0111  positive integer   Original code is complement code

                           -7                  0b0000 0111  //7

                                                0b1111 1000  // Inverse code

                                                0b1111 1001 // Complement -7 It's also 249   
Signed    

                   summary : The original code is a way of expression defined for the convenience of people to understand the habit of numbers , For example, the above example : Positive number 7 The binary number of the source code of is 0b0000 0111
   -7 The binary number of the original code of 0b0000 0111 , And their complement is different , Complement is the format of real data storage .   

         variable :

                 definition : type Variable name [= value ];

                 Role of type , Specify the size of memory , Specifies the type of data saved by the current variable , And variables are just aliases of this memory

                 initialization : I.e. simultaneous memory allocation

    2, Solid type

          double    Double precision     8 byte     After decimal point 15-17 position

          float       Single precision      4 byte    After decimal point 6 position

          constant :

                    2.3    Default is double

                    2.3    Single precision

                    2.3e+0 index 2.3*10 Of 0 Power

    3, character

         char    1 byte     The essence is unsigned integer     0-255

         constant     ‘a’         One character         The essence is ASCII code , One byte

         character : A symbol enclosed in single quotation marks

         character string : A sequence of characters in double quotes , with \0 end ( String is constant )

                      example :“asda” Yes 5 Characters , Contains a \0     

         Escape character :

                    Single quotation mark     ‘ \' ’     Is a character

                    Double quotes     ' \" '    

                    tab key      ‘ \t ’

                    Backspace key    ‘ \b ’

                    Alarm bell        ' \a '

                    enter        ‘ \r ’

                    Wrap        ' \n '

                    8 Base   '\ddd'  Must be three digits d For one 8 Number of decimal places
                   16 Base '\xhh'  Must be 2 Individual bit   h For one 16 Number of base bits

         

          character set :

                       ASCII 0-127 number , Number representing the character image to be drawn '\0' namely 0 number
                        '\0' == 0==NULL
       
                      GBK   Character set in mainland China
                      BIG5  Taiwan \ Hong Kong , Macao , Singapore , U.S.A
                      uncode  utf-8    qt android Etc utf-8 character set
                      utf-16
                      utf-24
                      utf-32  
               
                      'A' ==65 == '\x41' ='\101' == 0x41 == 0101
       
                      Arithmetic operation of characters
                       'A'+2;
       
                      '8'+2; //56+2
                      8+2;  //8+2
                      "8"+2  // address +2  The string itself is the 0 Character address   The input of instruction parameter is string
                      "asdf" The value is a Address of the memory       be careful : String is constant , The value of the string cannot be modified through this memory address

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