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#include <stdio.h>

int main()
{
	int i;
	char j;
	float k;
	
	i = 123;
	j = 'C';
	k = 3.14;
	
	printf("size of int is %d\n",sizeof(int));
	printf("size of i is %d\n",sizeof(i));
	printf("size of char is %d\n",sizeof(char));
	printf("size of j is %d\n",sizeof j);
	printf("size of float is %d\n",sizeof(float));
	printf("size of k is %d\n",sizeof k);
	
	return 0;
}

Code run results ：

Print the bytes occupied by each type separately ：

#include <stdio.h>

int main()
{
	printf("int = %d\n",sizeof(int));
	printf("short int = %d\n",sizeof(short));
	printf("long int = %d\n",sizeof(long));
	printf("long long int = %d\n",sizeof(long long));
	printf("char = %d\n",sizeof(char));
	printf("_Bool = %d\n",sizeof(_Bool));
	printf("float = %d\n",sizeof(float));
	printf("double = %d\n",sizeof(double));
	printf("long double = %d\n",sizeof(long double));
	
	return 0;
	
}

Running results （ The equipment is different , The results may be different ）：

3.signed and unsigned

signed： Stands for signed , The first bit represents positive and negative , The remaining represents the size , for example ：signed int The size range is -128-127.（ The default is signed）

unsigned： Represents an unsigned , All bits are size , No negative number , for example ：unsigned int The size range is ：0-255.

[signed] short [int]
unsigned short [int]
[signed] int
unsigned int
[signed] long [int]
unsigned long [int]
[signed] long long [int]
unsigned long long [int]

The code for ：

#include <stdio.h>

int main()
{
	short i;
	unsigned short j;
	
	i = -1;
	j = -1;
	
	printf("%d\n",i);//d For printing signed  
	printf("%u\n",j);//u For printing unsigned  
	
	return 0;
}

Running results ：

so , Print j when , The result is not what we expected -1, It is 65535, This is related to the value range of the data type .

Two 、 Value range of basic data type

1. bits

CPU The smallest unit that can be read is ： bits ,bit,b. Each bit can only store binary numbers , namely 0 and 1.

2. byte

Minimum addressing unit of memory mechanism ： byte ,Byte,B

notes ：1Byte = 8 bit

The maximum number that can be stored in a byte （ $2^{31}-1$ ） Expressed in binary as ：

The number is converted to decimal ：2147483647

Add ： Base number

Print $2^{32}-1$ , The code is as follows ：

# include <stdio.h>
#include <math.h>

int main()
{
	unsigned int result = pow(2,32) - 1;
	printf("result = %u\n",result);
	
	return 0;
}

Running results ：

Be careful ： If not add “unsigned”, The output is 2147483647. This is because by default int yes signed Type of , That is to say, the first bit on the left is the sign bit , So it must be added “unsigned” Make it an unsigned integer variable , bring 32 Bits are used to store values .

3. Sign bit

Deposit signed Type of storage unit , The first bit on the left indicates the sign bit . If the bit is 0, Indicates that the integer is a positive number ; If the bit is 1, Indicates that the integer is a negative number .
One 32 Bit integer variable , Remove the first sign bit on the left , The only remaining values are 31 A bit .

4. Complement code

The complement of a positive number is the binary form of the number .
The complement of negative numbers needs to be obtained through the following steps ：

（1） First obtain the binary form of the absolute value of the number

（2） And then 1 The value of step is inversed by bit （ Except the sign bit ）

（3） Finally, the second 2 Step value plus 1

for example ：

5. Value range of basic data type

data type	Number of bytes	Value range
char	1	-128~127
unsigned char2	1	0~255
short	2	-32768~32767
unsigned short	2	0~65535
int	4	-2147483648~2147483647
unsigned int	4	0~4294967295
long	4	-2147483648~2147483647
unsigned long	4	0~4294967295
long long	8	-9223372036854775808~9223372036854775807
unsigned long long	8	0~18446744073709551615

data type	Number of bytes	Value range （ The absolute value ）
float	4	1.1754910^-38~3.4028210^38
double	8	2.2250710^-308~1.7976910^308
long double	12	2.2250710^-308~1.7976910^308