std::cout statements evaluation order [duplicate]

Answer 1

Nothing did go wrong, but the pops get (in your case) evaluated from right to left if you put them all in one std::cout line. In general. the evaluation order is unspecified. For more detail on this see here.

So you correctly get the elements in reverse order of insertion and then -1 and then print them reversed.

Answer 2

In the last line of your code, you make several function calls (hidden, but each << operator is actually a function call). The evaluation of the parameters to these function calls is unspecified. So it is unspecified which "pop() function is called first.