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DSA SERIES — STACK USING LINKED LIST (IN C)
1. INTRODUCTION
A stack using a linked list works by treating the head of the linked list as the top of the stack. Every push inserts a new node at the beginning, and every pop removes from the beginning.
Why Linked List Stack?
-
No fixed size
-
Efficient insertion and deletion (O(1))
-
Memory used only when needed
2. NODE STRUCTURE (IMPORTANT)
struct Node {
int data; // value stored in the stack
struct Node* next; // pointer to next node
};
Explanation of Members:
-
data → Holds the stack element
-
next →
-
Points to the next node
-
For top node, next points to the node below it
-
For last node, next = NULL
-
3. STACK TOP POINTER
struct Node* top = NULL;
Meaning:
-
When
top == NULL, stack is empty -
Top always points to the most recently added node
4. PUSH OPERATION (INSERT AT BEGINNING)
void push(int value) {
struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
if (!newNode) {
printf("Memory allocation failed! Stack Overflow\n");
return;
}
newNode->data = value;
newNode->next = top; // new node points to previous top
top = newNode; // update top to new node
printf("%d pushed to stack\n", value);
}
Explanation:
-
A new node is created using malloc
-
newNode->next = toplinks node to existing stack -
top = newNodemakes new node the first element of stack
5. POP OPERATION (DELETE BEGINNING)
int pop() {
if (top == NULL) {
printf("Stack Underflow! Cannot pop\n");
return -1;
}
struct Node* temp = top;
int poppedValue = temp->data;
top = top->next; // move top to next node
free(temp); // delete old top node
return poppedValue;
}
Explanation:
-
If no node, underflow
-
Store top value
-
Move top pointer
-
Free removed node memory
6. PEEK / TOP ELEMENT
int peek() {
if (top == NULL) {
printf("Stack is Empty\n");
return -1;
}
return top->data;
}
7. DISPLAY STACK
void display() {
if (top == NULL) {
printf("Stack is Empty\n");
return;
}
struct Node* temp = top;
printf("Stack elements (Top to Bottom):\n");
while (temp != NULL) {
printf("%d ", temp->data);
temp = temp->next;
}
printf("\n");
}
8. COMPLETE PROGRAM — STACK USING LINKED LIST (C VERSION)
#include <stdio.h>
#include <stdlib.h>
struct Node {
int data;
struct Node* next;
};
struct Node* top = NULL;
void push(int value) {
struct Node* newNode = (struct Node*)malloc(sizeof(struct Node));
if (!newNode) {
printf("Memory allocation failed! Stack Overflow\n");
return;
}
newNode->data = value;
newNode->next = top;
top = newNode;
printf("%d pushed to stack\n", value);
}
int pop() {
if (top == NULL) {
printf("Stack Underflow! Cannot pop\n");
return -1;
}
struct Node* temp = top;
int poppedValue = temp->data;
top = top->next;
free(temp);
return poppedValue;
}
int peek() {
if (top == NULL) {
printf("Stack is Empty\n");
return -1;
}
return top->data;
}
void display() {
if (top == NULL) {
printf("Stack is Empty\n");
return;
}
struct Node* temp = top;
printf("Stack elements (Top to Bottom):\n");
while (temp != NULL) {
printf("%d ", temp->data);
temp = temp->next;
}
printf("\n");
}
int main() {
push(10);
push(20);
push(30);
display();
printf("Top element: %d\n", peek());
printf("Popped element: %d\n", pop());
display();
return 0;
}
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