2 stack to 1queue

    /* C program to implement queues using two stacks */

    #include <stdio.h>

    #include <stdlib.h>

    struct node

    {

        int data;

        struct node *next;

    };

    void push(struct node** top, int data);

    int pop(struct node** top);

    struct queue

    {

        struct node *stack1;

        struct node *stack2;

    };

    void enqueue(struct queue *q, int x)

    {

        push(&q->stack1, x);

    }

    void dequeue(struct queue *q)

    {

        int x;

        if (q->stack1 == NULL && q->stack2 == NULL) {

            printf("queue is empty");

            return;

        }

        if (q->stack2 == NULL) {

            while (q->stack1 != NULL) {

            x = pop(&q->stack1);

            push(&q->stack2, x);

            }

        }

        x = pop(&q->stack2);

        printf("%d\n", x);

    }

    void push(struct node** top, int data)

    {

        struct node* newnode = (struct node*) malloc(sizeof(struct node));

            if (newnode == NULL) {

                printf("Stack overflow \n");

                return;

            }

        newnode->data = data;

        newnode->next = (*top);

        (*top) = newnode;

    }

    int pop(struct node** top)

    {

        int buff;

        struct node *t;

        if (*top == NULL) {

            printf("Stack underflow \n");

            return;

        }

        else {

            t = *top;

            buff = t->data;

            *top = t->next;

            free(t);

            return buff;

        }

    }

    void display(struct node *top1,struct node *top2)

    {

        while (top1 != NULL) {

            printf("%d\n", top1->data);

            top1 = top1->next;

        }

        while (top2 != NULL) {

            printf("%d\n", top2->data);

            top2 = top2->next;

        }

    }

    int main()

    {

        struct queue *q = (struct queue*)malloc(sizeof(struct queue));

        int f = 0, a;

        char ch = 'y';

        q->stack1 = NULL;

        q->stack2 = NULL;

        while (ch == 'y'||ch == 'Y') {

            printf("enter ur choice\n1.add to queue\n2.remove

                   from queue\n3.display\n4.exit\n");

            scanf("%d", &f);

            switch(f) {

                case 1 : printf("enter the element to be added to queue\n");

                         scanf("%d", &a);

                         enqueue(q, a);

                         break;

                case 2 : dequeue(q);

                         break;

                case 3 : display(q->stack1, q->stack2);

                         break;

                case 4 : exit(1);

                         break;

                default : printf("invalid\n");

                          break;

            }

        }

    }