queueLinkedlist, C++ (gcc)

Language: Layout:

//g++  5.4.0
//someerror in f
#include <iostream>
using namespace std;

struct node 
{
    node *next;
    int val;
    
    
};

class queue
{
  node * f,*r;
    public:
    queue()
    {
    f=NULL;
        r=NULL;
    }
    void insert(int x)
    {
        node *temp=new node();
        temp->val=x;
        temp->next=NULL;
       
    if(isempty())
    {
        f=temp;
        r=f;
        
    }
        else
        {
        
        r->next=temp;
            r=temp;
        }
    }
    
    
    void del()
    {
    
    if(isempty())
    {
    cout<<"is empty";
        
    }
        else if(r==f)
        {
        r=f=NULL;
        }
        else
        {
        
        node *temp;
            temp=f;
            f=f->next;
            delete temp;
            
        
        }
    
    }
    
    bool isempty()
    {
    if(f==NULL)
    return true;
    return false;
    }

void display()
{

node *temp;
    temp=f;
    while(temp!=NULL)
    {
    cout<<temp->val<<" ";
        temp=temp->next;
    }
    
}
};

int main()
{
queue  q;
    q.insert(1);
       q.insert(6);
    q.insert(7);
      q.insert(3);
    q.insert(2);
  
    q.insert(4);
    q.insert(5);
    q.insert(7);
      q.del();
    q.del();
    /*   q.insert(10);
        
   q.insert(122);
   q.insert(123);

q.insert(7);

q.display();
  
        q.del();
    q.del();
        q.del();
    q.del();
        q.del();
    q.del();
        q.del();
    q.del();
        q.del();
        q.del();
    q.del();
    q.del();*/
     q.display();
}

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Compilation time: 0.43 sec, absolute running time: 0.19 sec, cpu time: 0.08 sec, memory peak: 3 Mb, absolute service time: 0,63 sec