stacks-1.c

#include<stdio.h>
#include<stdlib.h>
#include<limits.h>

struct Node {
	int data;
	struct Node* next;
};

struct Node* newNode(int data) {
	struct Node* node = (struct Node*) malloc(sizeof(struct Node));
	node->data = data;
	node->next = NULL;
	return node;
}

int isEmpty(struct Node* root) {
	return !root;
}

void push(struct Node** root, int data) {
	struct Node* node = newNode(data);
	node->next = *root;
	*root = node;
	printf("%d pushed to stack\n", data);
}

int pop(struct Node** root) {
	if(isEmpty(*root)) {
		return INT_MIN;
	}
	struct Node* temp = *root;
	*root = (*root)->next;
	int popped = temp->data;
	free(temp);
	return popped;
}

int peek(struct Node** root) {
	if(isEmpty(*root)) {
		return INT_MIN;
	}
	return (*root)->data;
}

int main() {
	struct Node* root = NULL;
	push(&root, 10);
	push(&root, 20);
	push(&root, 30);
	printf("%d popped from stack\n", pop(&root));
	printf("Top element is %d\n", peek(&root));
	return 0;
}