I think ++ has higher precedence over *, so it is evaluated first. You can make the first one work, if you put the brackets correctly.

The ++ may not work as you expect in this example. Try rewriting it like the other one.

You can't / don't. The solution set-up has direction in the comments about using the provided pointers positivesCount, and negativesSum:

  // Please store the positives count in the memory, pointed to
  // by the positivesCount parameter.
  
  // Please store the negatives sum in the memory, pointed to
  // by the negativesSum parameter.

You cannot modify any element of the array. You'll get an error if you try to.