c2955-使用“类”模板需要参数列表。 队列

Question

I'm trying to code a queue based on a list with templates, but I have a strange error and a don't know what to do whith it. I googled that error but I haven't find any answers that would be useful for me. Sorry for my English. Thanks for support.

#include <iostream>
#include <conio.h>
using namespace std;


template<class T>

class Node{
public: 
    Node(T obj){value=obj; next=NULL;};
Node* next;
T value;
};

template<class T>
class Queue{

    Node *top;
    Node *bottom;

public:
    Queue();
    void push(T obj);
    T pop();
     void print();
    ~Queue(){ if(next) delete next;};
    void delete_queue();




};

template<class T>Queue <T>::Queue(){
    top=bottom=NULL;

}




template<class T> void Queue <T>::push(T obj){

Node *newNode= new Node(obj);

if(bottom) bottom->next = newNode;
else { top=newNode; bottom=newNode;}   

}




    template<class T> T Queue <T>::pop(){

if(top){
    Node * del = top;
    T val = del-> value;
    top=top->next;
    delete del;
    cout<<"popped "<<val;
    return val;
}else {cout<<"Error"; return 0;}
    }


void main(){
int n=0, p;
char k;
Queue<int> *a=new Queue<int>();
while(1){
 cout<<"1.Push \n";
 cout<<"2.Pop \n";

 k=getch();
 switch(k){
      case '1':
          cout<<"Enter obj "<<endl;
          cin>>p;
          cout<<endl;
          a->push(p);

         break;
      case '2':
        a->pop();
         break;

}
}
}

Answer 1

You have to specify template arguments when you use a template

For example

class Queue{

    Node<T> *top;
    Node<T> *bottom;

or

template<class T> void Queue <T>::push(T obj){

Node<T> *newNode= new Node<T>(obj);

Also if you did not define name null yourself then I think you meant NULL or even better to use nullptr if you compiler supports this keyword. Otherwise this statement

top=bottom=null;

is invalid.

Also function main shall have return type int.

int main()

And it is not clear why you allocate class Queue in heap instead of simply define it as a local object of main. For example

Queue<int> a;