链接列表错误 - 未知数字和错误功能

I've been brushing up on data structures recently, specifically linked list, and was having some trouble determining the origin of some numbers. The number -2147483648 is shown twice each time the list is updated and it is always at the end of the list. I have no idea where this number comes from, but it is always present. It is worth nothing that when adding a new element to the tail of the list, the new value is placed between the two unknown nodes. I will highlight an example in the output. It is also worth noting that the list only accounts for one of the values. I will also highlight this in the output.I've been brushing up on data structures recent