โปรแกรม C++ ใช้งาน Circular Queue

Circular Queue เชื่อมตำแหน่งสุดท้ายกับแรกเป็นวงกลม ใช้ Array ขนาดคงที่

ตัวอย่างโค้ดสมบูรณ์

#include <iostream>
using namespace std;

const int MAX = 5;
int cqueue[MAX];
int front = -1, rear = -1;

void insertCQ(int val) {
    if ((front == 0 && rear == MAX-1) || (front == rear + 1)) {
        cout << "Queue Overflow\n";
        return;
    }
    if (front == -1) {
        front = rear = 0;
    } else if (rear == MAX - 1) {
        rear = 0;
    } else {
        rear++;
    }
    cqueue[rear] = val;
}

void deleteCQ() {
    if (front == -1) {
        cout << "Queue Underflow\n";
        return;
    }
    cout << "Element deleted: " << cqueue[front] << endl;
    if (front == rear) {
        front = rear = -1;
    } else if (front == MAX - 1) {
        front = 0;
    } else {
        front++;
    }
}

void displayCQ() {
    if (front == -1) {
        cout << "Queue is empty\n";
        return;
    }
    cout << "Queue elements: ";
    int f = front, r = rear;
    if (f <= r) {
        while (f <= r) cout << cqueue[f++] << " ";
    } else {
        while (f <= MAX-1) cout << cqueue[f++] << " ";
        f = 0;
        while (f <= r) cout << cqueue[f++] << " ";
    }
    cout << endl;
}

int main() {
    int ch, val;
    do {
        cout << "1)Insert 2)Delete 3)Display 4)Exit\nEnter choice: ";
        cin >> ch;
        switch (ch) {
            case 1: cout << "Input: "; 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;
}

การทำงานหลัก

• Insert: ตรวจ Overflow → Update Rear (Wrap around) → Store
• Delete: ตรวจ Underflow → Read Front → Update Front (Wrap around)
• Display: จัดการ 2 กรณี: Front ≤ Rear (Linear) หรือ Front > Rear (Wrapped)

C++ STL Alternative

ไม่มี Circular Queue โดยตรงใน STL แต่ใช้ std::deque หรือ Boost Circular Buffer ได้