<pre>
main(
)
</pre>

class Stack:
    def __init__(self, size=10):
        # 初始化一个固定大小的列表作为栈，并设置栈顶指针为-1
        self.stack = [None] * size
        self.top = -1

    def is_empty(self):
        # 判断栈是否为空
        return self.top == -1

    def is_full(self):
        # 判断栈是否已满
        return self.top == len(self.stack) - 1

    def push(self, item):
        # 如果栈未满，将元素压入栈，否则打印溢出信息
        if self.is_full():
            print("Stack Overflow")
        else:
            self.top += 1
            self.stack[self.top] = item

    def pop(self):
        # 如果栈非空，弹出栈顶元素并返回，否则打印下溢信息
        if self.is_empty():
            print("Stack Underflow")
        else:
            item = self.stack[self.top]
            self.top -= 1
            return item

    def peek(self):
        # 如果栈非空，返回栈顶元素，否则打印栈为空信息
        if not self.is_empty():
            return self.stack[self.top]
        else:
            print("Stack is empty")

def process_numbers():
    # 创建一个栈对象
    stack = Stack()
    while True:
        # 循环读取用户输入的整数
        try:
            num = int(input("Enter a number (-1 to end): "))
            # 将非-1的整数压入栈
            if num != -1:
                stack.push(num)
            # 当输入为-1且栈非空时，弹出栈顶元素并打印
            elif num == -1 and not stack.is_empty():
                print("Popped and printed:", stack.pop())
            # 当输入为-1且栈为空时，提示栈为空
            else:
                print("Stack is empty, nothing to pop.")
        except ValueError:
            # 捕获无效输入并提示
            print("Invalid input. Please enter an integer.")

# 运行处理数字的函数
process_numbers()

def is_paired(expression):
    # 创建一个空栈用于存储左括号
    stack = []
    # 定义括号映射关系
    mapping = {")": "(", "}": "{", "]": "["}

    # 遍历输入的表达式
    for char in expression:
        # 如果是左括号，压入栈
        if char in mapping.values():
            stack.append(char)
        # 如果是右括号，检查栈顶的左括号是否与之匹配，不匹配或栈为空则返回False
        elif char in mapping.keys():
            if not stack or mapping[char] != stack.pop():
                return False
    # 如果栈为空，说明括号匹配成功
    return not stack  # 如果栈为空，括号匹配正确

# 获取用户输入的表达式
expression = input("Enter an arithmetic expression: ")
# 检查括号是否正确配对
if is_paired(expression):
    print("The parentheses are correctly paired.")
else:
    print("The parentheses are not correctly paired.")