Circular Queue That has a display function that displays even numbers only - c++

Question

hi so i have this circular queue c++ program i need its display function only displays even inserted numbers only can someone here help please here's the code
i need a way that this program only displays even numbers only i'v been trying to use the %2==0 on some location that might make sense but mostly i get them wrong or empty
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#include <iostream>
using namespace std;
int cqueue[5];
int front = -1, rear = -1, n=5;
void insertCQ(int val) {
if ((front == 0 && rear == n-1) || (front == rear+1)) {
cout<<"Queue Overflow \n";
return;
}
if (front == -1) {
front = 0;
rear = 0;
} else {
if (rear == n - 1)
rear = 0;
else
rear = rear + 1;
}
cqueue[rear] = val ;
}
void deleteCQ() {
if (front == -1) {
cout<<"Queue Underflow\n";
return ;
}
cout<<"Element deleted from queue is : "<<cqueue[front]<<endl;
if (front == rear) {
front = -1;
rear = -1;
} else {
if (front == n - 1)
front = 0;
else
front = front + 1;
}
}
void displayCQ() {
int f = front, r = rear;
if (front == -1) {
cout<<"Queue is empty"<<endl;
return;
}
cout<<"Queue elements are :\n";
if (f <= r) {
while (f <= r){
cout<<cqueue[f]<<" ";
f++;
}
} else {
while (f <= n - 1) {
cout<<cqueue[f]<<" ";
f++;
}
f = 0;
while (f <= r) {
cout<<cqueue[f]<<" ";
f++;
}
}
cout<<endl;
}
int main() {
int ch, val;
cout<<"1)Insert\n";
cout<<"2)Delete\n";
cout<<"3)Display\n";
cout<<"4)Exit\n";
do {
cout<<"Enter choice : "<<endl;
cin>>ch;
switch(ch) {
case 1:
cout<<"Input for insertion: "<<endl;
cin>>val;
insertCQ(val);
break;
case 2:
deleteCQ();
break;
case 3:
displayCQ();
break;
case 4:
cout<<"Exit\n";
break;
default: cout<<"Incorrect!\n";
}
} while(ch != 4);
return 0;
}

Answer 1

Here's a quick example using std::queue:
#include <iostream>
#include <queue>
int main()
{
// This deque is declared just to more easily instantiate the queue
std::deque<int> deck{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
std::queue<int> q{deck};
while (!q.empty()) {
if (q.front() % 2 == 0) {
std::cout << q.front() << ' ';
}
q.pop();
}
std::cout << '\n';
}
You were on the right path using mod 2, but everything about your "queue" is not correct. To put it simply, you have not written a queue, and definitely not a circular queue.
Queues are FIFO data structures; first in, first out. Think of it like a tunnel. I will only add elements to one end, and I will only remove elements from the other. Everything in the middle does not matter, except to know the size of the queue. This means that the only visible elements are the first and last. If I want to see the second element of the queue, I must remove the first element.
The code you've written treats your array like a list instead where you have free access to all elements.
It's better to write an actual queue class, and I would hope that if you're writing data structures, that you are able to write a class.
Here's an extremely basic queue class that exhibits the behavior you are asking about. There is nothing circular about it. The word circular implies that your queue should be implemented with a circular linked list and not an array. It's worth noting that it requires at least C++11, but that really shouldn't be a problem today.
IMPORTANT
This code leaves out a lot of necessary error-checking. For example, back() will likely lead to undefined behavior if called on an empty queue, among other things. This was intentional to avoid a flat-out copy/paste being employed because cheating on homework is bad.
#include <array>
#include <iostream>
namespace Q {
class queue {
public:
int &front() { return m_arr[0]; }
int &back() { return m_arr[m_size - 1]; }
void push(int val) {
if (m_size < 5) {
m_arr[m_size] = val;
++m_size;
}
}
// Shifts entire array one to the left
void pop() {
if (m_size > 0) {
for (int i = 1; i < m_size; ++i) {
m_arr[i - 1] = m_arr[i];
}
--m_size;
}
}
bool empty() const { return m_size == 0; }
private:
std::array<int, 5> m_arr = {0};
int m_size = 0;
};
}; // namespace Q
int main() {
Q::queue q;
for (int i = 1; i <= 5; ++i) {
q.push(i);
}
while (!q.empty()) {
if (q.front() % 2 == 0) {
std::cout << q.front() << ' ';
}
q.pop();
}
std::cout << '\n';
}