Pre and post increments in C [closed]

Question

void main()
{
  int a = 1;
  a = ++a + ++a + ++a;
  printf("%d",a);
}

the above program gives the output 12.
What I have understood is that the variable 'a' is incremented thrice before it is cosidered for evaluation of the expression.

What I have'nt understood is why all the three increments are performed before any of them is evaluated in the expression.

Can anybody explain me with some simple equivalent low-level code about how the evaluatoin is done ?

Answer 1

That code is completely illegal, as it changes a several times between sequence points. Technically, that is undefined behaviour, the compiler can do whatever it pleases (and old gcc launched nethack in such cases).