stack.c

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

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

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

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

void push(struct StackNode *root){
	struct StackNode* stackNode = newNode(data);
	stackNode->next = *root;
	*root = stackNode;
	printf("%d pushed to stack", data);
}

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

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

int main()
{
    struct StackNode* 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;
}