Notes

// C program to Implement a stack
//using singly linked list
#include <stdio.h>
#include <stdlib.h>

// Declare linked list node

struct Node {
int data;
struct Node* link;
};
struct Node* top;

// Utility function to add an element data in the stack
// insert at the beginning
void push(int data)
{
// create new node temp and allocate memory
struct Node* temp;
temp = (struct Node*)malloc(sizeof(struct Node));

// check if stack (heap) is full. Then inserting an element would
// lead to stack overflow
if (!temp) {
printf("nHeap Overflow");
exit(1);
}

// initialize data into temp data field
temp->data = data;

// put top pointer reference into temp link
temp->link = top;

// make temp as top of Stack
top = temp;
}

// Utility function to check if the stack is empty or not
int isEmpty()
{
return top == NULL;
}

// Utility function to return top element in a stack
int peek()
{
// check for empty stack
if (!isEmpty(top))
return top->data;
else
exit(EXIT_FAILURE);
}

// Utility function to pop top element from the stack

void pop()
{
struct Node* temp;

// check for stack underflow
if (top == NULL) {
printf("nStack Underflow");
exit(1);
}
else {
// top assign into temp
temp = top;

// assign second node to top
top = top->link;

// destroy connection between first and second
temp->link = NULL;

// release memory of top node
free(temp);
}
}

void display() // remove at the beginning
{
struct Node* temp;

// check for stack underflow
if (top == NULL) {
printf("nStack Underflow");
exit(1);
}
else {
temp = top;
while (temp != NULL) {

// print node data
printf("%d->", temp->data);

// assign temp link to temp
temp = temp->link;
}
}
}

// main function

int main(void)
{
// push the elements of stack
push(11);
push(22);
push(33);
push(44);

// display stack elements
display();

// print top elementof stack
printf("nTop element is %dn", peek());

// delete top elements of stack
pop();
pop();

// display stack elements
display();

// print top elementof stack
printf("nTop element is %dn", peek());
return 0;
}