C ++：尝试将新节点添加到链接列表会产生“线程1：EXC_BAD_ACCESS（代码= 1，地址= 0x0）”错误

I'm writing a program for a homework assignment that creates and manipulates a linked list. I am encountering an "EXC_BAD_ACCESS" error with the Node::SetData function in Node.cpp, as well as with a line in List::Add_End in List.cpp (specifically "current->SetData(data);") and a line in main.cpp for some reason (specifically "// Add_End nodes to the list"). I assume that once the Node::SetData error is fixed, these other errors will resolve themselves.I'm writing a program for a homework assignment