线性结构-栈（Stack）

后进先出（Last-In-First-Out，LIFO）的原则，入栈（Push）：将元素插入到栈顶，出栈（Pop）：从栈顶删除元素，栈可以使用数组或链表实现。在实际应用中，栈常常用于处理递归、括号匹配、表达式求值等场景。

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

#define MAX_SIZE 100

typedef struct {
    int data[MAX_SIZE];
    int top;
} Stack;

void initialize(Stack* stack) {
    stack->top = -1;
}

void push(Stack* stack, int item) {
    if (stack->top == MAX_SIZE - 1) {
        printf("Stack is full. Cannot push element.\n");
        return;
    }
    stack->data[++stack->top] = item;
}

int pop(Stack* stack) {
    if (stack->top == -1) {
        printf("Stack is empty. Cannot pop element.\n");
        return -1;
    }
    return stack->data[stack->top--];
}

int peek(Stack* stack) {
    if (stack->top == -1) {
        printf("Stack is empty.\n");
        return -1;
    }
    return stack->data[stack->top];
}

int isEmpty(Stack* stack) {
    return stack->top == -1;
}

int size(Stack* stack) {
    return stack->top + 1;
}

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

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

    printf("Stack size: %d\n", size(&stack));
    printf("Top element: %d\n", peek(&stack));

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

    printf("Stack size: %d\n", size(&stack));

    return 0;
}