C language basics: a++ and ++a

(1) a + +

In C or other languages, the ++ sign means "self-addition", which means adding 1 to the original variable.
Case 1:

a = 0;
a++;

Then the value of a is 1.

By the same token, it means "self-subtracting".

Example 2:

a = 100;
a--;

Then the value of a is 99.

Note that there is no such thing as "self multiplication" or "self division" in programming languages.

Verification procedure:

#include <stdio.h>

int main()
{
  int a = 0; //  to a The assignment 
  a++;
  printf("After ++, a = %d\n", a);
  
  a = 100;  //  Back to the a The assignment 
  a--;
  printf("After --, a = %d\n", a);
  
  return 0;
}

Operation results:

After ++, a = 1
After --, a = 99

(2) + + a

In addition to a++ for self-addition, ++a also means self-addition. Same idea --a for self-subtraction

Verification procedure:

#include <stdio.h>

int main()
{
  int a = 0; //  to a The assignment 
  ++a;
  printf("After ++, a = %d\n", a);
  
  a = 100;  //  Back to the a The assignment 
  --a;
  printf("After --, a = %d\n", a);
  
  return 0;
}

Operation results:

After ++, a = 1
After --, a = 99

(3) differences between a++ and ++a

Since a++ and ++a are both added by a, are the two exactly the same?
Let's look at a program:

#include <stdio.h>

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

Operation results:

a = 0
a = 1
a = 2
a = 2
As can be seen from the operation results, a++ and ++a are different:
a++ reads the value of a first, then increments the value of a by 1;
++a increments the value of a by 1 before reading the value of a.