qusingstack.c

//Implement queue using stack
#include<stdio.h>
#include<stdlib.h>

//structure of a stack node
struct sNode{
    int data;
    struct sNode* next;
};

//Function to push item in stack
void push(struct sNode** top_ref, int new_data);

//Function to pop an item from stack
struct queue{
    struct sNode* stack1;
    struct sNode* stack2;
};

//Function to enQueue an item to queue
void enQueue(struct queue* q, int x){
    push(&q->stack1, x);
}

//Function to deQueue an item from queue
int deQueue(struct queue *q){
    int x;

    //If both stacks are empty, then error
    if(q->stack1 == NULL && q->stack2 == NULL){
        printf("Queue is empty");
        getchar();
        exit(0);
    }

    //Move elements from stack1 to stack2 only if stack2 is empty
    if(q-> stack2 == NULL){
        while(q->stack1 != NULL){
            x = pop(&q->stack1);
            push(&q->stack2, x);
        }
    }

    x = pop(&q->stack2);
    return x;
}

//Function to push an  item to stack
void push(struct sNode** top_ref, int new_data){

    //Allocate node
    struct sNode* new_node = (struct sNode*)malloc(sizeof(struct sNode));
    if(new_node == NULL){
        printf("Stack overflow \n");
        getchar();
        exit(0);
    }
    
    //put in the data
    new_node->data = new_data;

    //link the old list off the new node
    new_node->next = (*top_ref);

    //move the head to point to the new node
    (*top_ref) = new_node;
}

//Function to pop an item from stack
int pop(struct sNode** top_ref){
    int res;
    struct sNode* top;

    //If stack is empty them error
    if(*top_ref == NULL){
        printf("Stack underflow \n");
        getchar();
        exit(0);
    }
    else{
        top = *top_ref;
        res = top->data;
        *top_ref = top->next;
        free(top);
        return res;
    }
}

//main method
int main(){
    
    //Create a queue with items inserted by user
    struct queue* q = (struct queue*)malloc(sizeof(struct queue));
    q->stack1 = NULL;
    q->stack2 = NULL;
    printf("Enter the length of queue:");
    int n;
    scanf("%d", &n);
    for(int i = 0; i <= n; i++){
        enQueue(q, i);
    }

    //Dequeue items

}