else if(operatedCommand.equals('\u00d7'))
                 {
                     head = head*tail;
                     result.setText(Double.toString(head));
                     substitution = true;
                 }
                                // sub
                 else if(operatedCommand.equals('-'))
                 {
                     head = head-tail;
                     result.setText(Double.toString(head));
                     substitution = true;
                 }
                                // plus
                 else if(operatedCommand.equals('+'))
                {
                     head = head+tail;
                     result.setText(Double.toString(head));
                     substitution = true;
                 }
                                // pow
                 else if(operatedCommand.equals('pow'))
                {
                    head = Math.pow(head, tail);
                    result.setText(Double.toString(head));
                     substitution = true;
                }
                                // the Yth root of the X
                else if(operatedCommand.equals('XeY'))
                {
                    head = Math.pow(head, 1/tail);
                    result.setText(Double.toString(head));
                     substitution = true;    
                }
                                // modular
                else if(operatedCommand.equals('Mod'))
                {
                    head = head % tail;
                    result.setText(Double.toString(head));
                     substitution = true;
                }
             }
             preOperatedCommand = '=';
         }
        /*************************************************************
        *    set the action of the number
        **************************************************************/
        else if(actionCommand.equals('0'))
        {
            if(!(result.getText().equals('0') || result.getText().equals('-0')))
            {
                if(substitution)
                {
                    result.setText('0');
                }
                else
                    result.setText(result.getText() + '0');
            }
        }
        else if(actionCommand.equals('1'))
        {
            if(substitution)
            {
                result.setText('1');
                substitution = false;
            }
            else
                result.setText(result.getText() + '1');
        }
        else if(actionCommand.equals('2'))
        {
            if(substitution)
            {
                result.setText('2');
                substitution = false;
            }
            else
                result.setText(result.getText() + '2');
        }
        else if(actionCommand.equals('3'))
        {
            if(substitution)
            {
                result.setText('3');
                substitution = false;
            }
            else
                result.setText(result.getText() + '3');
        }
        else if(actionCommand.equals('4'))
        {
            if(substitution)
            {
                result.setText('4');
                substitution = false;
            }
            else
                result.setText(result.getText() + '4');
        }
        else if(actionCommand.equals('5'))
        {
            if(substitution)
            {
                result.setText('5');
                substitution = false;
            }
            else
                result.setText(result.getText() + '5');
        }
        else if(actionCommand.equals('6'))
        {
            if(substitution)
            {
                result.setText('6');
                substitution = false;
            }
            else
                result.setText(result.getText() + '6');
        }
        else if(actionCommand.equals('7'))
        {
            if(substitution)
            {
                result.setText('7');
                substitution = false;
            }
            else
                result.setText(result.getText() + '7');
        }
         else if(actionCommand.equals('8'))
         {
            if(substitution)
            {
                result.setText('8');
                substitution = false;
            }
            else
                result.setText(result.getText() + '8');
        }
         else if(actionCommand.equals('9'))
         {
            if(substitution)
            {
                result.setText('9');
                substitution = false;
            }
            else
                result.setText(result.getText() + '9');
        }
        else if(actionCommand.equals('.'))
        {
            if(result.getText().length() == 0)
                result.setText('0.');
                
            if(!(result.getText().contains('.')))
                result.setText(result.getText() + '.');
        }
        else if(actionCommand.equals('\u00b1'))
        {
            if(result.getText().charAt(0) != '-')
                result.setText('-' + result.getText());
            else
                result.setText(result.getText().substring(1));
        }
        else if(actionCommand.equals('C'))
        {
            result.setText('0');
            substitution = true;
        }
         
         /*************************************************************
        *    set the action of the arithmetic
        **************************************************************/
         // division
         else if(actionCommand.equals('\u00F7'))
         {
             head = Double.parseDouble(result.getText().trim());
             operatedCommand = '\u00F7';
             substitution = true;
             preOperatedCommand = '\u00F7';
         }
         // multiplication
         else if(actionCommand.equals('\u00d7'))
         {
             head = Double.parseDouble(result.getText().trim());
             operatedCommand = '\u00d7';
             substitution = true;
             preOperatedCommand = '\u00d7';
         }
                // sub
         else if(actionCommand.equals('-'))
         {
             head = Double.parseDouble(result.getText().trim());
             operatedCommand = '-';
             substitution = true;
             preOperatedCommand = '-';
         }
                // plus
         else if(actionCommand.equals('+'))
         {
             head = Double.parseDouble(result.getText().trim());
             operatedCommand = '+';
             substitution = true;
             preOperatedCommand = '+';
         }
                // backwards
         else if(actionCommand.equals('1/X'))
         {
             head = Double.parseDouble(result.getText().trim());
             if(head != 0)
                 result.setText(Double.toString(1/head));     
             else
             {
                 JOptionPane.showMessageDialog(this, 'Cannot divide by zero.');
                 head = 0.0;
                 tail = 0.0;
             }
         }
                // factorial
         else if(actionCommand.equals('X!'))
         {
             head = Double.parseDouble(result.getText().trim());
             result.setText(Double.toString(factorial(head)));    
         }
                // square
         else if(actionCommand.equals('sqr'))
         {
             head = Double.parseDouble(result.getText().trim());
             result.setText(Double.toString(head*head));    
         }
                // square root  
         else if(actionCommand.equals('\u221a'))
         {
             head = Double.parseDouble(result.getText().trim());
             if(head >= 0.0)
                 result.setText(Double.toString(Math.sqrt(head)));     
             else
             {
                 JOptionPane.showMessageDialog(this, 'Invalid input for function');
                 head = 0.0;
                 tail = 0.0;
             }    
         }
                // power
         else if(actionCommand.equals('pow'))
         {
             head = Double.parseDouble(result.getText().trim());
             operatedCommand = 'pow';
             substitution = true;
             preOperatedCommand = 'pow';
         }
                // the Yth of the X
         else if(actionCommand.equals('XeY'))
         {
             head = Double.parseDouble(result.getText().trim());
             operatedCommand = 'XeY';
             substitution = true;
             preOperatedCommand = 'XeY';    
         }
                // modular
         else if(actionCommand.equals('Mod'))
         {
             head = Double.parseDouble(result.getText().trim());
             operatedCommand = 'Mod';
             substitution = true;
             preOperatedCommand = 'Mod';    
         }
                // MS
         else if(actionCommand.equals('MS'))
         {
             variableMemory = Double.parseDouble(result.getText().trim());
         }
                // MR
         else if(actionCommand.equals('MR'))
         {
             result.setText(Double.toString(variableMemory));    
         }
                // MC
         else if(actionCommand.equals('MC'))
         {
             variableMemory = 0.0;    
         } 
         
     }
     /**
     * calculates and returns the factorial of the value
     *
     * @param value value of the root of the factorial
     *
     */
     public double factorial(double value)
     {
         if(value <= 1.0)
             return value;
         else
             return value*factorial(value-1);    
     } 
     /**
     * calculates and returns the check sum of the message.
     *
     * @param message message of the name whick entered by the user.
     */
     public long calChecksum(String message)
     {
         long check=0;
         
         for (int i=0;i<message.length();i++)
                  check += message.charAt(i);     
          return check;    
     }
     
     public static void main(String[] args)
     {
         Calculator calculator = new Calculator();
         calculator.pack();
         calculator.setVisible(true);    
     }
 }