The Stack
This article assumes that you have already read Linked-List in C and does not provide much explanation.
A stack is a data structure where each element is stacked on top of the previous element. The last element pushed is the first element accessed. It follows the LIFO (Last-In, First-Out) architecture. In other words, you cannot access any element on the bottom without taking elements out of the top.
Structure
The structure is the same as a singly linked-list.
struct Node { int data; struct Node *next;};Let's name the head of our stack as TOP.
struct Node *TOP;Operations
You can perform two operations on a stack:
- Pushing onto the stack
- Popping out of the stack
Pushing Onto The Stack
Pushing to the stack is the same as insert_at_beginning() from our singly linked-list.
void push(int item_to_insert) { struct Node *new_item = (struct Node *)malloc(sizeof(struct Node)); new_item->data = item_to_insert; new_item->next = NULL; if (TOP == NULL) { TOP = new_item; } else { struct Node *temp = TOP; TOP = new_item; TOP->next = temp; }}Popping Out Of The Stack
Popping out of the stack is just... our very simple delete_from_beginning() from
our singly linked-list.
void pop() { if (TOP == NULL) return; // Return in case of underflow else { struct Node *temp = TOP; TOP = TOP->next; free(temp); }}What We Have
#include <stdlib.h>struct Node { int data; struct Node *next;};struct Node *TOP;void push(int item_to_insert) { struct Node *new_item = (struct Node *)malloc(sizeof(struct Node)); new_item->data = item_to_insert; new_item->next = NULL; if (TOP == NULL) { TOP = new_item; } else { struct Node *temp = TOP; TOP = new_item; TOP->next = temp; }}void pop() { if (TOP == NULL) return; // Return in case of underflow else { struct Node *temp = TOP; TOP = TOP->next; free(temp); }}