DSA queue operations

#include <iostream>
#include <cstdlib>
using namespace std;
#define size 5
int queue[size];
int front=-1, rear = -1;
bool isEmpty()
{
return (rear == -1 && front == -1);
}
bool isFull()
{
    return (rear == size-1);
}
void Display()
{
    if(isEmpty())
        cout<<"\nQueue Underflow"<<endl;
    else
    {
        for(int i=front; i<=rear; i++)
            cout<<queue[i]<<" ";
    }
}
void Enque(int n)
{
    if(isFull())
        cout<<"\nQueue Overflow"<<endl;
else if(isEmpty())
{
queue[++rear] = n;
++front;
}
else
        queue[++rear] = n;
}
void Deque()
{
    if(isEmpty())
        cout<<"\nQueue Underflow"<<endl;
    else if(front == rear)
        front = rear = -1;
    else
    {
        queue[front++];
        Display();
    }
}
int main() {
int ch, val;
while(1)
{
cout<<"1. Enque"<<endl;
cout<<"2. Deque"<<endl;
cout<<"3. Display"<<endl;
cout<<"4. Exit"<<endl;
cout<<"\nEnter choice: ";
cin>>ch;
switch(ch)
{
case 1: cout<<"Enter a no.: ";
cin>>val;
Enque(val);
cout<<"\n";
break;
case 2: Deque();
cout<<"\n";
break;
case 3: Display();
cout<<"\n";
break;
case 4: exit(0); break;
default: cout<<"You entered wrong choice"<<endl; break;
}
cout<<"\n";
}
return 0;
}