How to learn C language and share super detailed experience (learning note 1 -- basic data types of C language)

Preface ：
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One 、 integer

According to the occupied memory size and the range of values that can be represented It can also be divided into short integers 、 Standard integer 、 Long integer 、 And long integer , Use keywords respectively short int、int、long int、long long int, Express .

1. Binary system 、 position 、 byte

The minimum storage unit of memory is bytes （Byte）, One byte has 8 position （Bit）( That is, one byte can be stored 8 Binary “0” or “1”).
High on the left , On the right is the low position , The highest bit is the sign bit ,（“0” For a positive number ,“1” It's a negative number ） All that's left is the data bits .
A byte 8 The range of values that bits can represent ranges from -128（1000 0000）~127（0111 1111）, common 256 individual .
Two bytes 16 The range of values that bits can represent ranges from -32768（1000 0000 0000 0000）~32767（0111 1111 1111 1111）, common 65536 individual .
According to different values , Use memory space of different size bytes , No waste of memory space , And can put the corresponding value , Truly accomplish “ make ”.

type	keyword	Take up memory	Value range
Short	short int	2 byte	-32768~32767
Standard integer	int	4 byte	-2147483648~2147483647
Long integer	long int	4 byte	-2147483648~2147483647
long long	long long int	8 byte	-9223372036854775808~9223372036854775807

2. Unsigned integer

For this kind of unsigned bit , Integer types that are all data bits , We call it unsigned integer , Its keyword is unsigned. The four types of integers mentioned earlier are all signed integers , They also have a keyword signed, But usually you don't have to write , That is, the default integer is signed , If you want to use unsigned integers , prefix unsigned Key words can be used .

type	keyword	Take up memory	Value range
Unsigned short	unsigned short int	2 byte	0~65535
Unsigned standard integer	unsigned int	4 byte	0~4294967295
Unsigned long	unsigned long int	4 byte	0~4294967295
Unsigned long integer	unsigned long long int	8 byte	0~18446744073709551615

Two 、 Real type

C This kind of numeric type with decimal point is called real type or floating-point number type in . Although there is only one word difference between real type and integer type , But it does have a completely different way of storing memory than integer .
The real type is stored in three segments ： Sign bit 、 Order code point 、 Data bits

Memory size and value range of real type

type	keyword	Take up memory	precision	Value range
Single precision floating point type	float	4 byte	6~7 Significant digits	-3.402823E+038~3.402823E+038
Double precision floating point type	double	8 byte	15~16 Significant digits	-1.797693E+308~1.797693E+308
Long double precision floating-point number type	long double

3、 ... and 、 Character

The character keyword is char, A character type is an integer type of a byte .
first C The language specifies that a byte integer is used as a character , To be more exact , Yes, it will 0~127 this 128 Use a positive integer as a character , This is the famous ASCII code （ American standard code for information exchange ）.
Character memory size and value range

type	keyword	Take up memory	Value range
Character	char	1 byte	-128~127
No sign character type	unsigned char	1 byte	0~255