Hi,

import java.awt.*;
import java.awt.event.*;
import java.awt.event.ActionListener;

class CalcFrame extends Frame {
CalcFrame( String str) {
// call to superclass
super(str);
// to close the calculator(Frame)
addWindowListener(new WindowAdapter() {
public void windowClosing (WindowEvent we) {
System.exit(0);
}
});
}
}

public class Calculator implements ActionListener, ItemListener {
// creating instances of objects
CalcFrame fr;
MenuBar menu;
Menu view, font;
MenuItem bold, regular;
CheckboxMenuItem basic ;
CheckboxGroup cbg;
Checkbox radians, degrees;
TextField display;
Button key[] = new Button[20]; // creates a button object array of 20
Button clearAll, clearEntry, round;
Button scientificKey[] = new Button[10]; // creates a button array of 8
// declaring variables
boolean addButtonPressed, subtractButtonPressed, multiplyButtonPressed;
boolean divideButtonPressed, decimalPointPressed, powerButtonPressed;
boolean roundButtonPressed = false;
double initialNumber; // the first number for the two number operation
double currentNumber = 0; // the number shown in the screen while it is being pressed
int decimalPlaces = 0;

// main function
public static void main (String args[]) {
// constructor
Calculator cal = new Calculator();
cal.makeCalculator();
}

public void makeCalculator() {
// size of the button
final int BWIDTH = 25;
final int BHEIGHT = 25;
int count =1;
// create frame for the calculator
fr = new CalcFrame("Simple Calculator");
// set the size
fr.setSize(300,270);
fr.setBackground(Color.pink);;
// create a menubar for the frame
menu = new MenuBar();
// add menu the menubar
view = new Menu("View");
font = new Menu ("Font");
// create instance of object for View menu
basic = new CheckboxMenuItem("Basic",true);
// add a listener to receive item events when the state of an item changes
basic.addItemListener(this);
// create instance of object for font menu
bold = new MenuItem("Arial Bold");
bold.addActionListener(this);

regular = new MenuItem("Arial Regular");
regular.addActionListener(this);
view.add(basic);
font.add(bold);
font.add(regular);

// add the menus in the menubar
menu.add(view);
menu.add(font);
// add menubar to the frame
fr.setMenuBar(menu);
// override the layout manager
fr.setLayout(null);
// set the initial numbers that is 1 to 9
for (int row = 0; row < 3; ++row) {
for (int col = 0; col < 3; ++col) {
// this will set the key from 1 to 9
key[count] = new Button(Integer.toString(count));
key[count].addActionListener(this);
// set the boundry for the keys
key[count].setBounds(30*(col + 1), 30*(row + 4),BWIDTH,BHEIGHT);
key[count].setBackground(Color.yellow);
// add to the frame
fr.add(key[count++]);
}
}

// Now create, addlistener and add to frame all other keys
key[0] = new Button("0");
key[0].addActionListener(this);
key[0].setBounds(30,210,BWIDTH,BHEIGHT);
key[0].setBackground(Color.yellow);
fr.add(key[0]);

//decimal
key[10] = new Button(".");
key[10].addActionListener(this);
key[10].setBounds(60,210,BWIDTH,BHEIGHT);
key[10].setBackground(Color.yellow);
fr.add(key[10]);

//equals to
key[11] = new Button("=");
key[11].addActionListener(this);
key[11].setBounds(90,210,BWIDTH,BHEIGHT);
key[11].setBackground(Color.yellow);
fr.add(key[11]);

//multiply
key[12] = new Button("*");
key[12].addActionListener(this);
key[12].setBounds(120,120,BWIDTH,BHEIGHT);
key[12].setBackground(Color.yellow);
fr.add(key[12]);

//divide
key[13] = new Button("/");
key[13].addActionListener(this);
key[13].setBounds(120,150,BWIDTH,BHEIGHT);
key[13].setBackground(Color.yellow);
fr.add(key[13]);

//addition
key[14] = new Button("+");
key[14].addActionListener(this);
key[14].setBounds(120,180,BWIDTH,BHEIGHT);
key[14].setBackground(Color.yellow);
fr.add(key[14]);

//subtract
key[15] = new Button("-");
key[15].addActionListener(this);
key[15].setBounds(120,210,BWIDTH,BHEIGHT);
key[15].setBackground(Color.yellow);
fr.add(key[15]);

//reciprocal
key[16] = new Button("1/x");
key[16].addActionListener(this);
key[16].setBounds(150,120,BWIDTH,BHEIGHT);
key[16].setBackground(Color.yellow);
fr.add(key[16]);

//power
key[17] = new Button("x^n");
key[17].addActionListener(this);
key[17].setBounds(150,150,BWIDTH,BHEIGHT);
key[17].setBackground(Color.yellow);
fr.add(key[17]);

//change sign
key[18] = new Button("+/-");
key[18].addActionListener(this);
key[18].setBounds(150,180,BWIDTH,BHEIGHT);
key[18].setBackground(Color.yellow);
fr.add(key[18]);

//factorial
key[19] = new Button("x!");
key[19].addActionListener(this);
key[19].setBounds(150,210,BWIDTH,BHEIGHT);
key[19].setBackground(Color.yellow);
fr.add(key[19]);

// CA
clearAll = new Button("CA");
clearAll.addActionListener(this);
clearAll.setBounds(30, 240, BWIDTH+20, BHEIGHT);
clearAll.setBackground(Color.yellow);
fr.add(clearAll);

// CE
clearEntry = new Button("CE");
clearEntry.addActionListener(this);
clearEntry.setBounds(80, 240, BWIDTH+20, BHEIGHT);
clearEntry.setBackground(Color.yellow);
fr.add(clearEntry);

// round
round = new Button("Round");
round.addActionListener(this);
round.setBounds(130, 240, BWIDTH+20, BHEIGHT);
round.setBackground(Color.yellow);
fr.add(round);

// set display area
display = new TextField("0");
display.setBounds(30,90,150,20);
display.setBackground(Color.white);

cbg = new CheckboxGroup();
degrees = new Checkbox("Degrees", cbg, true);
radians = new Checkbox("Radians", cbg, false);
degrees.addItemListener(this);
radians.addItemListener(this);

degrees.setBounds(185, 75, 3 * BWIDTH, BHEIGHT);
radians.setBounds(185, 95, 3 * BWIDTH, BHEIGHT);
degrees.setVisible(false);
radians.setVisible(false);
fr.add(degrees);
fr.add(radians);
fr.add(display);
fr.setVisible(true);
} // end of makeCalculator

public void actionPerformed(ActionEvent ae) {
String buttonText = ae.getActionCommand();
double displayNumber = Double.valueOf(display.getText()).doubleValue();

// if the button pressed text is 0 to 9
if((buttonText.charAt(0) >= '0') & (buttonText.charAt(0) <= '9')) {
if(decimalPointPressed) {
for (int i=1;i <=decimalPlaces; ++i)
currentNumber *= 10;
currentNumber +=(int)buttonText.charAt(0)- (int)'0';
for (int i=1;i <=decimalPlaces; ++i) {
currentNumber /=10;
}
++decimalPlaces;
display.setText(Double.toString(currentNumber));
}
else if (roundButtonPressed) {
int decPlaces = (int)buttonText.charAt(0) - (int)'0';
for (int i=0; i< decPlaces; ++i)
displayNumber *=10;
displayNumber = Math.round(displayNumber);

for (int i = 0; i < decPlaces; ++i) {
displayNumber /=10;

}

display.setText(Double.toString(displayNumber));
roundButtonPressed = false;
}
else {
currentNumber = currentNumber * 10 + (int)buttonText.charAt(0)-(int)'0';
display.setText(Integer.toString((int)currentNumber));
}
}

if(buttonText == "+") {
addButtonPressed = true;
initialNumber = displayNumber;
currentNumber = 0;
decimalPointPressed = false;
}

// if button pressed is subtract

if (buttonText == "-") {
subtractButtonPressed = true;
initialNumber = displayNumber;
currentNumber = 0;
decimalPointPressed = false;
}

// if button pressed is divide
if (buttonText == "/") {
divideButtonPressed = true;
initialNumber = displayNumber;
currentNumber = 0;
decimalPointPressed = false;
}

// if button pressed is multiply
if (buttonText == "*") {
multiplyButtonPressed = true;
initialNumber = displayNumber;
currentNumber = 0;
decimalPointPressed = false;
}

// if button pressed is reciprocal
if (buttonText == "1/x") {
// call reciprocal method
display.setText(reciprocal(displayNumber));
currentNumber = 0;
decimalPointPressed = false;
}

// if button is pressed to change a sign
if (buttonText == "+/-") {
// call changesign meyhod to change the sign
display.setText(changeSign(displayNumber));
currentNumber = 0;
decimalPointPressed = false;
}

// factorial button
if (buttonText == "x!") {
display.setText(factorial(displayNumber));
currentNumber = 0;
decimalPointPressed = false;
}
// power button
if (buttonText == "x^n") {
powerButtonPressed = true;
initialNumber = displayNumber;
currentNumber = 0;
decimalPointPressed = false;
}

// this will convert the numbers displayed to degrees
if (buttonText == "todeg")
display.setText(Double.toString(Math.toDegrees(displayNumber)));
// this will convert the numbers displayed to radians
if (buttonText == "torad")
display.setText(Double.toString(Math.toRadians(displayNumber)));

if (buttonText == "Pi") {
display.setText(Double.toString(Math.PI));
currentNumber =0;
decimalPointPressed = false;
}

if (buttonText == "Round")
roundButtonPressed = true;

// check if decimal point is pressed
if (buttonText == ".") {
String displayedNumber = display.getText();
boolean decimalPointFound = false;
int i;

decimalPointPressed = true;
// check for decimal point
for (i =0; i < displayedNumber.length(); ++i) {
if(displayedNumber.charAt(i) == '.') {
decimalPointFound = true;
continue;
}
}
if (!decimalPointFound)
decimalPlaces = 1;
}

if(buttonText == "CA"){
// set all buttons to false
resetAllButtons();
display.setText("0");
currentNumber = 0;
}

if (buttonText == "CE") {
display.setText("0");
currentNumber = 0;
decimalPointPressed = false;
}
if (buttonText == "E") {
display.setText(Double.toString(Math.E));
currentNumber = 0;
decimalPointPressed = false;
}

// the main action

if (buttonText == "=") {
currentNumber = 0;
// if add button is pressed
if(addButtonPressed)
display.setText(Double.toString(initialNumber + displayNumber));
// if subtract button is pressed
if(subtractButtonPressed)
display.setText(Double.toString(initialNumber - displayNumber));
// if divide button is pressed
if (divideButtonPressed) {
// check if the divisor is zero
if(displayNumber == 0) {
MessageBox mb = new MessageBox ( fr, "Error ", true, "Cannot divide by zero.");
mb.show();
}
else
display.setText(Double.toString(initialNumber/displayNumber));
}

// if multiply button is pressed
if(multiplyButtonPressed)
display.setText(Double.toString(initialNumber * displayNumber));
// if power button is pressed
if (powerButtonPressed)
display.setText(power(initialNumber, displayNumber));

// set all the buttons to false
resetAllButtons();
}

if (buttonText == "Arial Regular") {
for (int i =0; i < 10; ++i)
key[i].setFont(new Font("Arial", Font.PLAIN, 12));
}

if (buttonText == "Arial Bold") {
for (int i =0; i < 10; ++i)
key[i].setFont(new Font("Arial", Font.BOLD, 12));
}

} // end of action events

public void itemStateChanged(ItemEvent ie){
if (ie.getItem() == "Basic") {
basic.setState(true);
// scientific.setState(false);
fr.setTitle("Basic Calculator Example");
fr.setSize(200,270);
// check if the scientific keys are visible. if true hide them
if (scientificKey[0].isVisible()) {
for (int i=0; i < 8; ++i)
scientificKey[i].setVisible(false);
radians.setVisible(false);
degrees.setVisible(false);
}
}

} // end of itemState

public void resetAllButtons() {
addButtonPressed = false;
subtractButtonPressed = false;
multiplyButtonPressed = false;
divideButtonPressed = false;
decimalPointPressed = false;
powerButtonPressed = false;
roundButtonPressed = false;
}

public String factorial(double num) {
int theNum = (int)num;
if (theNum < 1) {
MessageBox mb = new MessageBox (fr, "Facorial Error", true,
"Cannot find the factorial of numbers less than 1.");
mb.show();
return("0");
}
else {
for (int i=(theNum -1); i > 1; --i)
theNum *= i;
return Integer.toString(theNum);
}
}

public String reciprocal(double num) {
if (num ==0) {
MessageBox mb = new MessageBox(fr,"Reciprocal Error", true,
"Cannot find the reciprocal of 0");
mb.show();
}
else
num = 1/num;
return Double.toString(num);
}

public String power (double base, double index) {
return Double.toString(Math.pow(base, index));
}

public String changeSign(double num) {
return Double.toString(-num);
}
}

class MessageBox extends Dialog implements ActionListener {
Button ok;
MessageBox(Frame f, String title, boolean mode, String message) {
super(f, title, mode);
Panel centrePanel = new Panel();
Label lbl = new Label(message);
centrePanel.add(lbl);
add(centrePanel, "Center");
Panel southPanel = new Panel();
ok = new Button ("OK");
ok.addActionListener(this);
southPanel.add(ok);
add(southPanel, "South");
pack();
addWindowListener (new WindowAdapter(){
public void windowClosing (WindowEvent we) {
System.exit(0);
}
});
}
public void actionPerformed(ActionEvent ae) {
dispose();
}
}

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