PTC Software Development Engineer interview questions

few questions about knowledge in C about char* and char [], and in C++ about constructors and destructors and virtual functions, and then i was asked the trapping rain water question with O(1) space without the need to code it, just to see the way of thinking

The interview lasted about an hour and was on C\C++ ,very basic questions but require deep understanding he asked me about something related to how the stack works when running the code in the question and also their was a question related to data structures