multiple '++' working in variables, and pointers

Question

This is what I think the ++ operator does

1. a++; // a+=1 after calculating this line
2. ++a; // a+=1 before calcuating this lin

Answer 1

You're not supposed to do more than one increment in arguments to a function.. because the order they can be evaluated in is ambiguous. The result of such code is undefined.

Meaning: printf("%d,%d,%d,%d\n",a++,a++,++a,++a); Should be written as

a++; a++;
++a; ++a;
printf("%d, %d, %d, %d\n", a, a, a, a);

Try and fix that first and see if the results are still confusing.

More generally, you should only have one increment between a pair of sequence points.

Edit: Chris is right, there's no point writing four increments in the middle of nowhere. To better answer your question: For a function void f(int) and void g(int), with int a=0,

f(++a) = f(1);
f(a++) = f(0);
g(++a, ++a) = g(???); // undefined!

So, increment at most once in the argument to a function.