设计一个低、中、高级的带界面的PC端的程序，低级可以计算十道10以内的数学加减法题，中级可以计算十道100以内的数学加减法题，高级可以计算十道1000以内的数学加减法题，计算每正确一次加一分，错误则不得分，计算结束时，分数为7分及以上则为闯关成功，7分一下则为闯关失败。

好的，以下是基本的设计思路：

1. 界面设计：可以使用GUI库（如PyQt、Tkinter）来设计带有交互式界面的小游戏。

2. 随机生成题目：根据用户所选的难度等级，程序可以随机生成对应难度的加减法题目。

3. 计分规则：每回答一个问题，程序会根据用户的回答情况（正确或错误）来判断是否加分。正确回答加1分，错误回答不得分。

4. 闯关机制：程序会根据用户的得分情况来判断是否通过本次闯关。当得分为7分或以上时，闯关成功，否则闯关失败。

5. 程序流程：根据用户所选的难度等级，程序会自动生成对应数量的数学题目，并在界面上呈现出来。用户需要在规定的时间内完成所有的题目，并得到相应的得分。

您可以参考以下代码实现：

import random
import time
from PyQt5.QtWidgets import QApplication, QWidget, QPushButton, QLabel, QLineEdit, QVBoxLayout, QHBoxLayout, QRadioButton, QGroupBox, QMessageBox

class MathGame(QWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle('Math Game')
        self.setGeometry(300, 300, 500, 300)
        self.score = 0
        self.timer = None

        self.difficulty_group = QGroupBox('Difficulty Level')
        self.difficulty_group_layout = QVBoxLayout()
        self.difficulty_group.setLayout(self.difficulty_group_layout)

        self.low_rbtn = QRadioButton('Low')
        self.mid_rbtn = QRadioButton('Mid')
        self.high_rbtn = QRadioButton('High')
        self.difficulty_group_layout.addWidget(self.low_rbtn)
        self.difficulty_group_layout.addWidget(self.mid_rbtn)
        self.difficulty_group_layout.addWidget(self.high_rbtn)
        self.low_rbtn.setChecked(True)

        self.start_btn = QPushButton('Start')
        self.start_btn.clicked.connect(self.start_game)

        self.timer_lbl = QLabel('Time Left: 0')
        self.score_lbl = QLabel('Score: 0')
        self.question_lbl = QLabel('Question:')

        self.answer_edit = QLineEdit()

        self.submit_btn = QPushButton('Submit')
        self.submit_btn.clicked.connect(self.submit_answer)

        self.main_layout = QVBoxLayout()
        self.main_layout.addWidget(self.difficulty_group)
        self.main_layout.addWidget(self.start_btn)
        self.main_layout.addWidget(self.timer_lbl)
        self.main_layout.addWidget(self.score_lbl)
        self.main_layout.addWidget(self.question_lbl)
        self.main_layout.addWidget(self.answer_edit)
        self.main_layout.addWidget(self.submit_btn)

        self.setLayout(self.main_layout)

    def start_game(self):
        self.score = 0
        self.score_lbl.setText(f'Score: {self.score}')
        self.timer = 60
        self.timer_lbl.setText(f'Time Left: {self.timer}')
        self.start_btn.setEnabled(False)

        difficulty_level = ''
        if self.low_rbtn.isChecked():
            difficulty_level = 'low'
        elif self.mid_rbtn.isChecked():
            difficulty_level = 'mid'
        elif self.high_rbtn.isChecked():
            difficulty_level = 'high'

        self.question_list = self.generate_questions(difficulty_level)
        self.current_question = 0
        self.show_question()

        self.timer_thread = TimerThread(self)
        self.timer_thread.timer_signal.connect(self.update_timer)
        self.timer_thread.start()

    def show_question(self):
        question = self.question_list[self.current_question]
        self.question_lbl.setText(f'Question: {question}')

    def submit_answer(self):
        answer = self.answer_edit.text()
        if answer == str(eval(self.question_list[self.current_question])):
            self.score += 1
            self.score_lbl.setText(f'Score: {self.score}')
            QMessageBox.information(self, 'Correct', 'Your answer is correct!')
        else:
            QMessageBox.warning(self, 'Wrong', 'Your answer is wrong!')

        self.current_question += 1
        if self.current_question < len(self.question_list):
            self.show_question()
        else:
            self.end_game()

    def end_game(self):
        self.timer_thread.terminate()
        if self.score >= 7:
            QMessageBox.information(self, 'Success', 'You pass the game!')
        else:
            QMessageBox.warning(self, 'Fail', 'You fail the game!')

        self.start_btn.setEnabled(True)

    def generate_questions(self, difficulty_level):
        question_list = []
        if difficulty_level == 'low':
            for i in range(10):
                a = random.randint(0, 10)
                b = random.randint(0, 10)
                operator = random.choice(['+', '-'])
                question_list.append(f'{a} {operator} {b}')
        elif difficulty_level == 'mid':
            for i in range(10):
                a = random.randint(0, 100)
                b = random.randint(0, 100)
                operator = random.choice(['+', '-'])
                question_list.append(f'{a} {operator} {b}')
        elif difficulty_level == 'high':
            for i in range(10):
                a = random.randint(0, 1000)
                b = random.randint(0, 1000)
                operator = random.choice(['+', '-'])
                question_list.append(f'{a} {operator} {b}')

        return question_list

    def update_timer(self, time_left):
        self.timer_lbl.setText(f'Time Left: {time_left}')

class TimerThread(QThread):
    timer_signal = pyqtSignal(int)

    def __init__(self, parent=None):
        super().__init__(parent=parent)
        self.time_left = 60

    def run(self):
        while self.time_left > 0:
            self.time_left -= 1
            self.timer_signal.emit(self.time_left)
            time.sleep(1)

if __name__ == '__main__':
    app = QApplication([])
    math_game = MathGame()
    math_game.show()
    app.exec_()

这是一个基本的PC端数学小游戏，难度等级分为低、中、高三个等级，用户可以选择不同的难度等级来挑战不同难度的数学题目。程序会根据用户所选的难度等级来生成相应数量的数学题目，并在界面上呈现出来。用户需要在规定的时间内完成所有的题目，并得到相应的得分。程序会根据用户的得分情况来判断是否通过本次闯关。当得分为7分或以上时，闯关成功，否则闯关失败。