Stack using Two Queues in C++

This C++ program implements a stack data structure using two queue data structures. A stack data structure foolows the principle of LIFO(Last Element in First Element Out).

Here is the source code of the C program to displays the popped values from a stack in LIFO mode. The C++ program is successfully compiled and run on DevCpp, a C++ compiler. The program output is also shown below.

```
/*
```

 * C++ Program to Implement Stack using Two Queues

```
 */
```
```
#include<stdio.h>
```
```
#include<iostream>
```
```
#include<conio.h>
```
```
using namespace std;
```
```
struct queue1
```
```
{
```
```
    queue1 *next1;
```
```
    int data1;
```

}*front1 = NULL, *rear1 = NULL, *q1 = NULL, *p1 = NULL, *np1 = NULL;

```
struct queue2
```
```
{
```
```
    queue2 *next2;
```
```
    int data2;
```

}*front2 = NULL, *rear2 = NULL, *q2 = NULL, *p2 = NULL, *np2 = NULL;

```
void enqueue1(int x)
```
```
{     
```
```
    np1 = new queue1;
```
```
    np1->data1 = x;
```
```
    np1->next1 = NULL;
```
```
    if (front1 == NULL)
```
```
    {
```
```
        rear1 = np1;
```
```
        rear1->next1 = NULL;
```
```
        front1 = rear1;
```
```
    }
```
```
    else
```
```
    {
```
```
        rear1->next1 = np1;
```
```
        rear1 = np1;
```
```
        rear1->next1 = NULL;
```
```
    }
```
```
}
```
```
int dequeue1()
```
```
{
```
```
    int x;
```
```
    if (front1 == NULL)
```
```
    {
```

        cout<<"no elements present in queue\n";

```
    }
```
```
    else
```
```
    {
```
```
        q1 = front1;
```
```
        front1 = front1->next1;
```
```
        x = q1->data1;
```
```
        delete(q1);
```
```
        return x;
```
```
    }
```
```
}
```
```
void enqueue2(int x)
```
```
{
```
```
    np2 = new queue2;
```
```
    np2->data2 = x;
```
```
    np2->next2 = NULL;
```
```
    if (front2 == NULL)
```
```
    {
```
```
        rear2 = np2;
```
```
        rear2->next2 = NULL;
```
```
        front2=rear2;
```
```
    }
```
```
    else
```
```
    {
```
```
        rear2->next2 = np2;
```
```
        rear2 = np2;
```
```
        rear2->next2 = NULL;
```
```
    }
```
```
}
```
```
int dequeue2()
```
```
{
```
```
    int x;
```
```
    if (front2 == NULL)
```
```
    {
```

        cout<<"no elements present in queue\n";

```
    }
```
```
    else
```
```
    {
```
```
        q2 = front2;
```
```
        front2 = front2->next2;
```
```
        x = q2->data2;
```
```
        delete(q2);
```
```
        return x;
```
```
    }
```
```
}        
```
```
int main()
```
```
{
```
```
    int n, x, i = 0;
```

    cout<<"Enter the number of elements to be entered into stack\n";

```
    cin>>n;
```
```
    while (i < n)
```
```
    {
```

        cout<<"enter the element to be entered\n";

```
        cin>>x;
```
```
        enqueue1(x);
```
```
        i++;
```
```
    }
```
```
    cout<<"\n\nElements popped\n\n";
```

    while (front1 != NULL || front2 != NULL)

```
    {
```
```
        if (front2 == NULL)
```
```
        {
```

            while (front1->next1 != NULL)

```
            {
```
```
                enqueue2(dequeue1());
```
```
            }
```
```
            cout<<dequeue1()<<endl;
```
```
        }
```
```
        else if (front1 == NULL)
```
```
        {
```

            while (front2->next2 != NULL)

```
            {
```
```
                enqueue1(dequeue2());
```
```
            }
```
```
            cout<<dequeue2()<<endl;
```
```
        }
```
```
    }
```
```
    getch();
```
```
}
```

 
Output
 
Enter the number of elements to be entered into stack
7
enter the element to be entered
3
enter the element to be entered
9
enter the element to be entered
1
enter the element to be entered
0
enter the element to be entered
6
enter the element to be entered
4
enter the element to be entered
2
 
 
Elements popped
 
2
4
6
0
1
9
3

Sanfoundry Global Education & Learning Series – 1000 C++ Programs.

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