Why doesn't a+++++b work?

Question

int main ()
{
   int a = 5,b = 2;
   printf(\"%d\",a+++++b);
   return 0;
}

This code gives the following error:

error: lval

Answer 1

I think the compiler sees it as

c = ((a++)++)+b

++ has to have as an operand a value that can be modified. a is a value that can be modified. a++ however is an 'rvalue', it cannot be modified.

By the way the error I see on GCC C is the same, but differently-worded: lvalue required as increment operand.