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1.1 Integer classification
Include ： Basic integers int
Short short int
Long integer long int
Double long integers long long int C99
1.1 Extension type
[signed] short [int] Signed short integers
unsigned short [int] Unsigned Short
[signed] int Signed basic integer
unsigned [int] Unsigned Basic integers
[signed] long [int] Signed long integer
unsigned long [int] Unsigned Long integer
[signed] long long [int] Signed double long integer （C99 newly added ）
unsigned long long [int] Unsigned Double long integers （C99 newly added ）
1.3 The representation of integers
By polarity ： Positive numbers 、 Negative and zero .
In hexadecimal ： Binary system 、 octal 、 Decimal system 、 Hexadecimal etc .
1.4 The storage form of integers
In the computer memory, it is in accordance with Binary system Complement code form Storage Of .
(1) Original code
Binary source code ： Sign bit + Value bits
highest Symbol bit
Positive numbers ：0
negative ：1
(2) Example of original code

just Count Original code 、 Inverse code 、 Complement code all identical
(3) The inverse of a negative number 、 Complement code
Inverse code : Keep the sign bit of the negative original code unchanged , The value is inversed bit by bit .
Complement code : Add the negative number to the inverse code 1 That is, its complement .

2 Various base numbers and their conversion

2.1 Base judgment basis
Prefix method ： stay C in , Generally, the base is determined according to the prefix .
Prefix 0（ zero ） octal , Be careful ： Numbers 0, Non alphabetic o
Prefix 0x or 0X Hexadecimal
Default Decimal system
2.2 Decimal system - - > Binary system
2.3 octal
Numbers and rules ：0~7 must With Numbers 0 start , Every eight enters one.
give an example 1： Octal number 037 Represents the decimal number :
$3\times 8^{1}+7\times 8^{0}=31$
give an example 2： Decimal number 22 It can be expressed as ：026,
verification ： $6\times 8^{0}+2\times 8^{1}=22$
2.4 Hexadecimal
Numbers and rules ： from 0~9、A~F(a~f)16 Number , Every 16 to one .
give an example 1：0x1f、0x1F、0X1f or 0X1F, The corresponding decimal numbers are $1\times 16^{1}+15\times 16^{0}=31$
give an example 2： Decimal number 22 Can be expressed as ：0x16 or 0X16 : $6\times 16^{0}+1\times 16^{1}=22$

3 Each integer type and the number of bytes it occupies

3.1 Bits and bytes
position （bit）： Processing data Smallest unit , Can only 0 or 1.
byte （Byte）： Processing data Basic unit , Usually a byte in the system is 8 position . namely 1 Byte=8 bit
3.2 Factors affecting the number of bytes
Influencing factors ： Machine number 、C Compiler, etc. .
give an example ：32 Bit system ,Turbo C Environment int 2 byte .32 Bit system ,VC++6.0 Environment int 4 byte .
3.3 Number of bytes occupied by each type
short 2 byte
int 2 or 4 byte
long 4 byte
long long 8 byte
Tools ：sizeof The operator calculates the number of bytes occupied by each type in the environment
sizeof(int) sizeof(long)
3.4 Number of bytes occupied by each type
C The standard does not specify the specific number of bytes occupied by each type , It is only specified that the number of bytes occupied by each integer type meets the following relationship ：
sizeof(short) <= sizeof(int) <= sizeof(long) <= sizeof(long long)

4 Comprehensive case

4.1 All integer output controllers
%hd In decimal Short
%d In decimal Basic integers
%u In decimal Unsigned integer
%ld In decimal Long integer
%lo In octal Long integer
%lh In hex Long integer
4.2 Case study

#include<stdio.h>

int main(void)

{

     unsigned int un_a=2500000000; 
     long l_b=65539;
     printf("In this system:\n");
     printf("short  has %d bytes.\n",sizeof(short));
     printf("int    has %d bytes.\n",sizeof(int));
     printf("long  has %d bytes.\n",sizeof(long));
     printf("un_a = %u not %d\n",un_a,un_a);
     printf("l_b = %ld not %hd\n",l_b,l_b);
     return 0;

}