How to Implement stack in C?

You can implement a stack data structure in C using an array or a linked list.

1. Array

#include <stdio.h>
#include <stdbool.h>

#define MAX_SIZE 100

// Define the stack structure
typedef struct {
    int data[MAX_SIZE];
    int top;
} Stack;

// Function to initialize the stack
void initialize(Stack *stack) {
    stack->top = -1; // Set the top of the stack to -1 to indicate an empty stack
}

// Function to check if the stack is empty
bool isEmpty(Stack *stack) {
    return stack->top == -1;
}

// Function to check if the stack is full
bool isFull(Stack *stack) {
    return stack->top == MAX_SIZE - 1;
}

// Function to push an element onto the stack
bool push(Stack *stack, int item) {
    if (isFull(stack)) {
        printf("Stack is full. Cannot push.\n");
        return false;
    }
    stack->data[++stack->top] = item;
    return true;
}

// Function to pop an element from the stack
int pop(Stack *stack) {
    if (isEmpty(stack)) {
        printf("Stack is empty. Cannot pop.\n");
        return -1; // Return a sentinel value to indicate an error
    }
    return stack->data[stack->top--];
}

// Function to get the top element of the stack without popping it
int peek(Stack *stack) {
    if (isEmpty(stack)) {
        printf("Stack is empty. No top element.\n");
        return -1; // Return a sentinel value to indicate an error
    }
    return stack->data[stack->top];
}

int main() {
    Stack stack;
    initialize(&stack);

    // Push some elements onto the stack
    push(&stack, 10);
    push(&stack, 20);
    push(&stack, 30);

    // Print and pop elements from the stack
    while (!isEmpty(&stack)) {
        printf("Top element: %d\n", peek(&stack));
        printf("Popped element: %d\n", pop(&stack));
    }

    return 0;
}

2. LinkedList

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

// Define a structure for a single node in the linked list
typedef struct Node {
    int data;
    struct Node* next;
} Node;

// Define the stack structure with a pointer to the top of the stack
typedef struct {
    Node* top;
} Stack;

// Function to initialize the stack
void initialize(Stack* stack) {
    stack->top = NULL;
}

// Function to check if the stack is empty
bool isEmpty(Stack* stack) {
    return stack->top == NULL;
}

// Function to push an element onto the stack
void push(Stack* stack, int item) {
    Node* newNode = (Node*)malloc(sizeof(Node));
    if (newNode == NULL) {
        printf("Memory allocation failed. Cannot push.\n");
        return;
    }
    newNode->data = item;
    newNode->next = stack->top;
    stack->top = newNode;
}

// Function to pop an element from the stack
int pop(Stack* stack) {
    if (isEmpty(stack)) {
        printf("Stack is empty. Cannot pop.\n");
        return -1; // Return a sentinel value to indicate an error
    }
    Node* topNode = stack->top;
    int item = topNode->data;
    stack->top = topNode->next;
    free(topNode);
    return item;
}

// Function to get the top element of the stack without popping it
int peek(Stack* stack) {
    if (isEmpty(stack)) {
        printf("Stack is empty. No top element.\n");
        return -1; // Return a sentinel value to indicate an error
    }
    return stack->top->data;
}

// Function to free the memory used by the stack
void destroy(Stack* stack) {
    while (!isEmpty(stack)) {
        pop(stack);
    }
}

int main() {
    Stack stack;
    initialize(&stack);

    // Push some elements onto the stack
    push(&stack, 10);
    push(&stack, 20);
    push(&stack, 30);

    // Print and pop elements from the stack
    while (!isEmpty(&stack)) {
        printf("Top element: %d\n", peek(&stack));
        printf("Popped element: %d\n", pop(&stack));
    }

    // Free the memory used by the stack
    destroy(&stack);

    return 0;
}