Can you explain how does this code work?

Question

#include <stdio.h>
int main()
{
int a = 2, c=3;
a += --c + c++ ;
printf("%d %d ", a, c);
c += ++a + --a;
printf("%d %d", a, c);
return 0;
}

Answer 1

Two words, undefined behaviour
Output vary on the compiler implementation.

It happens when you mix data modification and access in a single execution point. Modern compilers, like one in SoloLearn will warn you this, had the option been enabled.