Queue

#include <iostream>
using namespace std;

struct node {
   int data;
   struct node *next;

};

struct node* front = NULL;
struct node* rear = NULL;
struct node* temp;

int prime(int num)
{
    int ct=0;

    for(int i=2; i<=num/2; i++)
    {
        if(num%i==0)
            ct++;
    }
    if(num == 1) return 0;
    if(ct>0)
        return 0;
    else
        return 1;
}
void Enqueue()
{
   int val,num;
   cout<<"How many elements do you Insert in queue ?"<<endl;
   cin >> num;
   cout << "Insert the elements: ";
   while(num--)
   {
       cin>>val;
       int p=prime(val);
       if(p){
           if (rear == NULL) {
              rear = new node;
              rear->next = NULL;
              rear->data = val;
              front = rear;
           } else {
              temp=new node;
              rear->next = temp;
              temp->data = val;
              temp->next = NULL;
              rear = temp;
           }
       }
   }
}
void Dequeue()
{
   temp = front;
   if (front == NULL) {
      cout<<"Oops!Queue is empty. May be you insert non-prime number!"<<endl;
      return;
   }
   else
   if(front->data > 30){
       if (temp->next != NULL) {
          temp = temp->next;
          cout<<front->data<<" has been deleted from the queue!"<<endl;
          delete(front);
          front = temp;
       } else {
          cout<<front->data<<" has been deleted from the queue!"<<endl;
          delete(front);
          front = NULL;
          rear = NULL;
       }
   }
   else
   {
       cout << "Can't be deleted because the value isn't greater than 30" << endl;
       return;
   }
}
void Display()
{

   temp = front;
   if ((front == NULL) && (rear == NULL)) {
      cout<<"Queue is empty. May be you insert non-prime number!"<<endl;
      return;
   }
   cout<<"Queue elements are: ";
   while (temp != NULL) {
      cout<<temp->data<<" ";
      temp = temp->next;
   }
   cout<<endl;
}
int main()
{
   int choice;
   cout<<"1) Enqueue"<<endl;
   cout<<"2) Dequeue"<<endl;
   cout<<"3) Display"<<endl;

while(1)
{
   cout<<"Enter your choice : "<<endl;

   cin>>choice;
   switch (choice) {
      case 1: Enqueue();
         break;
      case 2: Dequeue();
         break;
      case 3: Display();
         break;
      default: cout<<"Invalid choice"<<endl;
   }
}

   return 0;
}