Stack LIFO Principles

A Stack is a Last-In, First-Out (LIFO) data structure. Elements can only be added (push) or removed (pop) from the top of the stack.

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C Code Implementation

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>
#include <stdbool.h>

#define MAX_CAPACITY 5

typedef struct {
    int items[MAX_CAPACITY];
    int top;
} Stack;

void initStack(Stack *s) {
    s->top = -1;
}

bool isFull(const Stack *s) {
    return s->top == MAX_CAPACITY - 1;
}

bool isEmpty(const Stack *s) {
    return s->top == -1;
}

bool push(Stack *s, int value) {
    if (isFull(s)) {
        printf("Stack Overflow! Cannot push %d.\n", value);
        return false;
    }
    s->items[++(s->top)] = value;
    printf("Pushed %d to stack.\n", value);
    return true;
}

int pop(Stack *s) {
    if (isEmpty(s)) {
        printf("Stack Underflow! Stack is empty.\n");
        return -1;
    }
    return s->items[(s->top)--];
}

int peek(const Stack *s) {
    if (isEmpty(s)) return -1;
    return s->items[s->top];
}

int main() {
    Stack myStack;
    initStack(&myStack);

    push(&myStack, 10);
    push(&myStack, 20);
    push(&myStack, 30);

    printf("Top element: %d\n", peek(&myStack));

    printf("Popped: %d\n", pop(&myStack));
    printf("Popped: %d\n", pop(&myStack));

    return 0;
}

Sample Output

text (ISO Standard)
Copy
Pushed 10 to stack.
Pushed 20 to stack.
Pushed 30 to stack.
Top element: 30
Popped: 30
Popped: 20

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Complexity Analysis

• Push / Pop / Peek: O(1) constant time operations.
• Space Complexity: O(MAX_CAPACITY) fixed buffer.

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Related Data Structures

• Compare with dynamic node structures in Singly Linked List in C.
• Master structures in Structures in C.