In C operation associativity is as such for increment, decrement and assignment.
2. postfix ++ and --
3. prefix ++ and --
16. Direct assignment =
<
The postfix operator a++ will increment a and then return the original value i.e. similar to this:
{ temp=a; a=a+1; return temp; }
and the prefix ++a will return the new value i.e.
{ a=a+1; return a; }
This is irrelevant to the operator precedence.
(And associativity governs whether a-b-c equals to (a-b)-c or a-(b-c).)