import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class calculator extends JFrame implements ActionListener {

    private JTextField display;
    private String equation = "";
    private boolean newNumber = true;

    public calculator() {
        setTitle("简易计算器");
        setSize(300, 400);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(new BorderLayout());

        display = new JTextField("0");
        display.setEditable(false);
        display.setHorizontalAlignment(JTextField.RIGHT);
        display.setFont(new Font("Arial", Font.BOLD, 24));
        display.setPreferredSize(new Dimension(300, 60));
        add(display, BorderLayout.NORTH);

        JPanel panel = new JPanel();
        panel.setLayout(new GridLayout(5, 4));

        String[] buttons = {
                "7", "8", "9", "/",
                "4", "5", "6", "*",
                "1", "2", "3", "-",
                "0", ".", "=", "+",
                "C", "%" // 添加取余按钮
        };

        for (String label : buttons) {
            JButton button = new JButton(label);
            button.setFont(new Font("Arial", Font.BOLD, 18));
            button.addActionListener(this);
            panel.add(button);
        }

        add(panel, BorderLayout.CENTER);
        setLocationRelativeTo(null);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();

        if ("0123456789.".indexOf(command) >= 0) {
            if (newNumber) {
                display.setText(command);
                newNumber = false;
            } else {
                display.setText(display.getText() + command);
            }
        } else if ("+-*/%".indexOf(command) >= 0) { // 添加 % 运算符
            equation = display.getText() + command;
            display.setText("0");
            newNumber = true;
        } else if (command.equals("=")) {
            try {
                equation += display.getText();
                double result = new ExpressionEvaluator(equation).evaluate();
                if (result == (long) result) {
                    display.setText(String.valueOf((long) result));
                } else {
                    display.setText(String.valueOf(result));
                }
                newNumber = true;
            } catch (Exception ex) {
                display.setText("Error");
            }
        } else if (command.equals("C")) {
            display.setText("0");
            equation = "";
            newNumber = true;
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            calculator calc = new calculator();
            calc.setVisible(true);
        });
    }
}

class ExpressionEvaluator {
    private int pos = -1;
    private int ch;
    private final String str;

    public ExpressionEvaluator(String str) {
        this.str = str;
    }

    private void nextChar() {
        ch = (++pos < str.length()) ? str.charAt(pos) : -1;
    }

    private boolean eat(int charToEat) {
        while (ch == ' ') nextChar();
        if (ch == charToEat) {
            nextChar();
            return true;
        }
        return false;
    }

    public double evaluate() {
        nextChar();
        double x = parseExpression();
        if (pos < str.length()) throw new RuntimeException("Unexpected: " + (char)ch);
        return x;
    }

    private double parseExpression() {
        double x = parseTerm();
        for (;;) {
            if (eat('+')) x += parseTerm(); // addition
            else if (eat('-')) x -= parseTerm(); // subtraction
            else return x;
        }
    }

    private double parseTerm() {
        double x = parseFactor();
        for (;;) {
            if (eat('*')) x *= parseFactor(); // multiplication
            else if (eat('/')) x /= parseFactor(); // division
            else if (eat('%')) x %= parseFactor(); // modulus
            else return x;
        }
    }

    private double parseFactor() {
        if (eat('+')) return parseFactor(); // unary plus
        if (eat('-')) return -parseFactor(); // unary minus

        double x;
        int startPos = this.pos;
        if (eat('(')) { // parentheses
            x = parseExpression();
            eat(')');
        } else if ((ch >= '0' && ch <= '9') || ch == '.') { // numbers
            while ((ch >= '0' && ch <= '9') || ch == '.') nextChar();
            x = Double.parseDouble(str.substring(startPos, this.pos));
        } else {
            throw new RuntimeException("Unexpected: " + (char)ch);
        }

        if (eat('^')) x = Math.pow(x, parseFactor()); // exponentiation
        return x;
    }
}
//changes