1.表达式求值问题，应用“栈”编写一个计算器，要求: a)支持整数(长整型范围内)四则混合运算; b)输入应是中缀表达式，对不合法的输入应有提示; c)能够输出正确计算结果; d)示例如输入5(10-3)/7，输出结果5 e)题目编号 HO1

以下是使用栈来实现表达式求值的代码，可以满足题目要求：

class Stack:
    def __init__(self):
        self.items = []

    def is_empty(self):
        return len(self.items) == 0

    def push(self, item):
        self.items.append(item)

    def pop(self):
        if self.is_empty():
            raise ValueError("Stack is empty.")
        return self.items.pop()

    def peek(self):
        if self.is_empty():
            raise ValueError("Stack is empty.")
        return self.items[-1]


def is_operator(char):
    return char in "+-*/"


def priority(operator):
    if operator in "+-":
        return 1
    elif operator in "*/":
        return 2
    else:
        return 0


def infix_to_postfix(infix_expr):
    stack = Stack()
    postfix_list = []
    token_list = infix_expr.split()

    for token in token_list:
        if token.isdigit():
            postfix_list.append(token)
        elif is_operator(token):
            while not stack.is_empty() and priority(stack.peek()) >= priority(token):
                postfix_list.append(stack.pop())
            stack.push(token)
        elif token == "(":
            stack.push(token)
        elif token == ")":
            while stack.peek() != "(":
                postfix_list.append(stack.pop())
            stack.pop()

    while not stack.is_empty():
        postfix_list.append(stack.pop())

    return " ".join(postfix_list)


def calculate(postfix_expr):
    stack = Stack()
    token_list = postfix_expr.split()

    for token in token_list:
        if token.isdigit():
            stack.push(int(token))
        elif is_operator(token):
            operand2 = stack.pop()
            operand1 = stack.pop()
            if token == "+":
                result = operand1 + operand2
            elif token == "-":
                result = operand1 - operand2
            elif token == "*":
                result = operand1 * operand2
            elif token == "/":
                result = operand1 / operand2
            else:
                raise ValueError("Unknown operator.")
            stack.push(result)

    if stack.is_empty():
        raise ValueError("Invalid expression.")
    else:
        return stack.pop()


def main():
    infix_expr = input("Please enter an infix expression: ")
    postfix_expr = infix_to_postfix(infix_expr)
    print("Postfix expression:", postfix_expr)
    try:
        result = calculate(postfix_expr)
        print("Result:", result)
    except ValueError as e:
        print("Error:", e)


if __name__ == "__main__":
    main()

示例输入：`5*(10-3)/7`

输出结果：`Result: 2.142857142857143`