Puzzle #1 (based on C++17)
#include <cstdint>

auto foo(uint8_t n)
{
    while (true) { ++n; }
    return n;
}

int main()
{
  return foo(0);
}
With given code, pick one answer:
Guaranteed to return 0 from main
Guaranteed to return something other than 0 from main
Undefined bahaviour
Implementation defined
Will not compile