Small notes - integer improvement (C language)

Write it at the front

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Hello everyone , Here are the fan's little notes , This note briefly records the concept of plastic enhancement 、 Meaning and simple examples , Thank you for your support .

Plastic surgery improves

• Shaping lifting concept

C The integer arithmetic operation of always takes at least the default integer type （int） The accuracy of . In order to achieve this precision , The character type and short integer operands in the expression are converted to normal integers before use , This conversion is called integer
promote .

• Plastic surgery improves the meaning

The integer operation of expression should be in CPU In the corresponding computing device of ,CPU Inner integer arithmetic unit (ALU) The byte length of the operands of
It is commonly int Byte length of , It's also CPU The length of the general register of .
therefore , Even two char The addition of types , stay CPU When executing, it should be converted to CPU The standard length of an inner integer operand
degree .
Universal CPU（general-purpose CPU） It is difficult to realize two directly 8 Direct addition of bits and bytes （ Although machine instructions
There may be such byte addition instructions in ）. therefore , Various lengths in expressions may be less than int The integer value of the length , You have to turn first
Replace with int or unsigned int, Then it can be sent in CPU To perform the operation .

• Shaping promotion rules
  ️ The high-order supplementary sign bit during the lifting of the integer , Unsigned types are high complement 0.
  
• Example ：
  With int The type and unsigned int Type to print char Type data process

int main()
{
    
	char a = -128;
	//char  Range -128—127
	printf("%d %u",a, a);
	return 0;
}

Running results ：

a The storage process of the value of ：

10000000 00000000 00000000 10000000    -128 The original code of 
  Reverse the original code 
11111111 11111111 11111111 01111111    -128 The inverse of 
 One plus one 
11111111 11111111 11111111 10000000    -128 Complement 
a Length bit 1 byte             a:10000000    Complement truncation , Take the last byte 

Take out a Value ：

                            10000000   a
 11111111 11111111 11111111 10000000   a Plastic surgery improves 
  The complement minus one 
 11111111 11111111 11111111 01111111    After promotion a The inverse of 
 The sign bits remain the same , Reverse other bits 
 10000000 00000000 00000000 10000000    After promotion a The original code of 
 With int Form printing a, The highest bit is the sign bit 
 The value printed is -128
 With unsigned int Form printing ： The highest bit is not a sign bit 
 The value printed is 4294967168

Last

To get the whole content of this note , Original code 、 The inverse code and complement code were discussed in the last article, so this time we will talk about them roughly .
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