The difference between the increment and decrement operators before and after variables i+, +i, I –, – I

Auto increment and auto decrement operator yes Composite operators A simpler way of writing

Variable a Add yourself 1 Can be expressed as ：

a=a+1;

Composite operators notation

a+=1;

Self - increment operator notation

a++;
++a;

Correspondingly, there are Self - subtracting operator notation

a--;
--a

After the completion of self increase and self decrease , Meeting Replace old value with new value Save in current Variable in .

The result of self increasing and self decreasing must have a variable to receive , Therefore, self increase and self decrease can only be applied to Variable , Cannot be for numbers or expressions .

Pre auto increment （ Self reduction ） Self increasing after and （ Self reduction ） The difference between ：
An example ： Output i The value after self increment and are respectively i++ and ++i The assignment of j Value , Analyze the difference between the two kinds of autoincrement

#include <stdio.h>

int main() { 
    
	int i = 5, j;
	j = i++;
	printf("i=%d,j=%d\n", i, j);
	i = 5;
	j = ++i;
	printf("i=%d,j=%d\n", i, j);
	return 0;
}

According to the observation results i All values change to 6, however j But they are assigned to 5 and 6, That is to say, the difference between pre auto increment and post auto increment is that the value is assigned after auto increment , The other one assigns values first and then increases automatically .
Mnemonics ：
【 According to the assignment character ‘=’ After Variable i In the form of Judge i Whether the value before or after auto increment is assigned to j】
if 【++i】, Then put ++i As a whole , Put the self increasing i value （++i） Assign to j（ Self increment and then assignment );
if 【i】, First put i Value is assigned to j, let i Self increasing （ First assign value and then auto increment ）.
（ Self subtraction as above ）