Queue in c++

#include<bits/stdc++.h>
using namespace std;
int sizeq = 5, qu[5],front = -1, rear = -1;

bool isFull()
{
    if(rear==(sizeq-1)) return true;
    else return false;
}
bool isEmpty()
{
    if(rear<0) return true;
    else return false;
}

void enq(int n)
{
    if(isFull()) cout<<"Overflow\n";
    else if(isEmpty())
    {
        front=0;
        rear=0;
        qu[rear]=n;
    }
    else
    {
        rear++;
        qu[rear]=n;
    }
}
void dq(){
    if(isEmpty()) cout<<"Underflow\n";
    else {
        front++;
    }
}
void display(){
    if(isEmpty()){
       cout<<"Underflow\n";
    }
    else if(isFull()) {
        cout <<"Overflow\n";
    }
    else{
        cout<<"Queue is :: \n  ";
        for (int i = front; i <= rear ; i++ ){
            cout<<qu[i]<<" ";
        }
    }
}

int main()
{

    enq(5);
    enq(6);
    enq(7);
    enq(8);
    dq();
    display();
    return 0;
}