stackUsingQueue.c

// Stack Using Queue

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#define CAPACITY 5

int f1 = -1;
int r1 = -1;
int f2 = -1;
int r2 = -1;
int queue1[CAPACITY];
int queue2[CAPACITY];

bool isEmpty1()
{
    if (f1 == -1 || f1 > r1)
    {

        return true;
    }
    return false;
}

bool isEmpty2()
{
    if (f2 == -1 || f2 > r2)
    {

        return true;
    }
    return false;
}

bool isFull()
{
    if (r1 == CAPACITY - 1)
    {
        return true;
    }
    return false;
}

void enQueue(int data)
{

    if (isFull())
    {
        printf("Stack is Full");
        return;
    }
    if (f1 == -1)
    {
        f1++;
    }
    while (!isEmpty1())
    {
        if (f2 == -1)
        {
            f2++;
        }
        queue2[++r2] = queue1[r1--];
    }

    queue1[++r1] = data;

    while (!isEmpty2())
    {
        if (f1 == -1)
        {
            f1++;
        }
        queue1[++r1] = queue2[r2--];
    }
}

void deQueue()
{

    if (isEmpty1())
    {
        printf("Queue is Empty");
        return;
    }
    f1++;
}

int peek()
{

    if (isEmpty1())
    {
        printf("Queue is Empty");
        exit(0);
    }
    return queue1[f1];
}

void printQueue()
{

    for (int i = r1; i >= f1; i--)
    {
        printf("%d  ", queue1[i]);
    }
    printf("\n");
}

void main()
{
    enQueue(5);
    enQueue(15);
    enQueue(20);
    enQueue(25);
    enQueue(30);

    printQueue();

    deQueue();
    deQueue();

    printQueue();

    printf("Element at first : %d\n", peek());
}