使用类和类型

我正在尝试这个新项目，这是我不久前被介绍的，但我不确定这里发生了什么。我确信我可以将 int 存储在 int 变量中，但它告诉我我无法从 int 转换为学生，我不确定它想告诉我什么。这里有人可以向我解释一下这到底想告诉我什么或我错过了什么吗？

#include <iostream>
using namespace std;
class student
{
public:
    int id;            //student ID number
    string name;       //student’s name
    string university; //student’ university
};

//student list is a doubly linked list of students. 
class studentList
{
private:
    class node
    {
    public:
        student data;
        node * next;
        node * prev;
    };
    node * head;
public:
    studentList()
    {
        head = NULL;
    }
    //be sure to free all dynamically allocated memory!
    ~studentList();
    //return true if the list is empty, false if not
    bool empty()
    {
        if(head == NULL)
            return true;
        else
            return false;
    };
    //insert student s into the front of the linked list
    void push(student s)
    {
        node * nodeptr;
        nodeptr = new node();
        nodeptr->data = s;
        nodeptr->next = head;
        head = nodeptr;
        nodeptr->prev = head;
        if (nodeptr->next != NULL)
            nodeptr->next->prev = nodeptr;
    };
    //remove and return the student at the front of the list
    student pop()
    {
        node * nodeptr;
        int y;
        nodeptr = head;
        if (head->next != NULL)
            head->next->prev = head;
        head = head->next;
        y = nodeptr->data.id;
        delete nodeptr;
        return y;
    };
    //locate and remove the student with given ID number
    void removeStudent(int id);
    //locate and return a copy of the student with given ID number
    student getStudent(int id);
    //arrange students into increasing based on either ID or name.  If
    //variable 'field' has value "id", sort into increasing order by id.
    //If 'field' has value "name", sort into alphabetical order by name.
    void sort(string field);
    //a test function to simply display the list of students to the screen
    //in the order they appear in the list.
    void display();
};