P6-P15: init

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

P9.java

@@ -0,0 +1,154 @@
+import javax.swing.*;
+import java.awt.*;
+import java.awt.event.ActionEvent;
+import java.awt.event.ActionListener;
+
+public class P9 extends JFrame {
+    private JTextField displayField;
+
+    public P9() {
+        setTitle("Scientific Calculator");
+        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+        setResizable(true);
+
+        displayField = new JTextField();
+        displayField.setPreferredSize(new Dimension(300, 30));
+        displayField.setEditable(false);
+
+        JPanel buttonPanel = new JPanel(new GridLayout(6, 4, 10, 10));
+
+        String[] buttonLabels = {
+                "7", "8", "9", "/",
+                "4", "5", "6", "*",
+                "1", "2", "3", "-",
+                "0", ".", "=", "+",
+                "sin", "cos", "tan", "sqrt",
+                "e", "^", "pi", "clr"
+        };
+
+        for (String label : buttonLabels) {
+            JButton button = new JButton(label);
+            button.addActionListener(new ButtonClickListener());
+            buttonPanel.add(button);
+        }
+
+        setLayout(new FlowLayout());
+        add(displayField);
+        add(buttonPanel);
+
+        pack();
+        setLocationRelativeTo(null);
+        setVisible(true);
+    }
+
+    private class ButtonClickListener implements ActionListener {
+        public void actionPerformed(ActionEvent event) {
+            String command = event.getActionCommand();
+            String expression = displayField.getText();
+            if ("=".equals(command)) {
+                calculate();
+            } else if ("clr".equals(command)) {
+                displayField.setText("");
+            } else if ("sin".equals(command)) {
+                displayField.setText(String.valueOf(Math.sin(Double.parseDouble(expression))));
+            } else if ("cos".equals(command)) {
+                displayField.setText(String.valueOf(Math.cos(Double.parseDouble(expression))));
+            } else if ("tan".equals(command)) {
+                displayField.setText(String.valueOf(Math.tan(Double.parseDouble(expression))));
+            } else if ("sqrt".equals(command)) {
+                displayField.setText(String.valueOf(Math.sqrt(Double.parseDouble(expression))));
+            } else {
+                displayField.setText(displayField.getText() + command);
+            }
+        }
+
+        private void calculate() {
+            String expression = displayField.getText();
+            try {
+                double result = evaluateExpression(expression);
+                displayField.setText(String.valueOf(result));
+            } catch (NumberFormatException e) {
+                displayField.setText("Error");
+            }
+        }
+
+        private double evaluateExpression(String expression) {
+            return new Object() {
+                int pos = -1, ch;
+
+                void nextChar() {
+                    ch = (++pos < expression.length()) ? expression.charAt(pos) : -1;
+                }
+
+                boolean eat(int charToEat) {
+                    while (ch == ' ') nextChar();
+                    if (ch == charToEat) {
+                        nextChar();
+                        return true;
+                    }
+
+                    return false;
+                }
+
+                double parse() {
+                    nextChar();
+                    double x = parseExpression();
+                    if (pos < expression.length()) throw new RuntimeException("Unexpected character: " + (char) ch);
+                    return x;
+                }
+
+                double parseExpression() {
+                    double x = parseTerm();
+                    while(true) {
+                        if (eat('+')) x += parseTerm();
+                        else if (eat('-')) x -= parseTerm();
+                        else return x;
+                    }
+                }
+
+                double parseTerm() {
+                    double x = parseFactor();
+                    while (true) {
+                        if (eat('*')) x *= parseFactor();
+                        else if (eat('/')) x /= parseFactor();
+                        else return x;
+                    }
+                }
+
+                double parseFactor() {
+                    if (eat('+')) return parseFactor();
+                    if (eat('-')) return -parseFactor();
+
+                    double x;
+                    int startPos = this.pos;
+                    if (eat('(')) {
+                        x = parseExpression();
+                        eat(')');
+                    } else if ((ch >= '0' && ch <= '9') || ch == '.') {
+                        while ((ch >= '0' && ch <= '9') || ch == '.') nextChar();
+                        x = Double.parseDouble(expression.substring(startPos, this.pos));
+                    } else if (eat('e')) {
+                        x = Math.E;
+                    } else if (eat('p')) {
+                        eat('i');
+                        x = Math.PI;
+                    } else {
+                        throw new RuntimeException("Unexpected character: " + (char) ch);
+                    }
+
+                    if (eat('^')) x = Math.pow(x, parseFactor());
+
+                    return x;
+                }
+            }.parse();
+        }
+    }
+
+    public static void main(String[] args) {
+        SwingUtilities.invokeLater(new Runnable() {
+            public void run() {
+                new P9();
+            }
+        });
+    }
+}