A9a_CLLstack.c

/* Implement stack using Circular Linked List. */
#include<stdlib.h>
#include<stdio.h>

typedef struct cllstack {
	int data;
	struct cllstack * ptr;
}cllstack;

cllstack * head = NULL;

cllstack * createnode() {
	cllstack * newnode = (cllstack *)malloc(sizeof(cllstack));
	printf("Enter the data element : ");
	scanf("%d" , &newnode->data);
	newnode->ptr = NULL;
	return newnode;
}

void push() {
	if(head == NULL) {
		head = createnode();
		head->ptr = head;
	}
	else {
		cllstack * temp = createnode();
		temp->ptr = head->ptr;
		head->ptr = temp;
	}
	printf("Element successfully pushed.\n");
}

void pop() {
	if(head == NULL)
		printf("Stack is empty.\n");
	else if(head->ptr == head) {
		printf("Element %d successfully popped out.\n" , head->data);
		free(head);
		head = NULL;
	}
	else {
		cllstack * temp = head->ptr;
		printf("Element %d successfully deleted.\n" , temp->data);
		temp = temp->ptr;
		head->ptr = temp;
	}
}

void display() {
	if(head == NULL)
		printf("Stack is empty.\n");
	else {
		cllstack * strt = head->ptr ;
		printf("Elements of stack are : ");
		while(strt != head) {
			printf("%d  " , strt->data);
			strt = strt->ptr;
		}
		printf("%d  " , strt->data);
		printf("\n");
		strt = NULL;
	}
}

void main() {
	int choice , flag = 1 ;
	printf("Enter the operation to be performed.\n");
	while(flag) {
		printf("1.Push \t 2.Pop \t 3.Display \t 4.Exit  : ");
		scanf("%d" , &choice);
		switch(choice) {
			case 1 : push();
				 	 break;

			case 2 : pop();
				 	 break;

			case 3 : display();
				  	 break;

			case 4 : flag = 0 ;
				     break;
			 
			default : printf("Invalid input.\n");
				 	  break;
		}
	}
}