// Simple calculator using char.
// Program features user-friendly, useful messages and prompts.
// Think - INPUT - PROCESSING - OUTPUT.

import javax.swing.JOptionPane;

public class SimpleCalculator
{
   public static void main(String[]args)
   {
      String operatorS;
      char operatorC;
      double firstNumber = 0.0, secondNumber = 0.0, total = 0.0;
	  
      // INPUT
      // String values converted to double values
      firstNumber = Double.parseDouble(JOptionPane.showInputDialog("Enter the first number"));
      secondNumber = Double.parseDouble(JOptionPane.showInputDialog("Enter the second number"));
      
      operatorS = JOptionPane.showInputDialog("Enter the operator" +"\n" +  "+ to add" + "\n" 
      + "- to subtract" + "\n" +  "* to multiply"  +  "\n" +  "/ to divide.");
      
	  // PROCESSING
      // Converts String to char.A;so ensures data validation of the operator.
      operatorC = operatorS.charAt(0);
      
      if (operatorC == '+')
         total = firstNumber + secondNumber;
         
      else if (operatorC == '-')
         total = firstNumber - secondNumber;
         
      else if (operatorC == '*')
         total = firstNumber * secondNumber;
         
      else if (operatorC == '/')
         total = firstNumber / secondNumber;         
      else {
         // System exit if the operator is bad.
         JOptionPane.showMessageDialog(null, "Unrecognisable operator." + "\n" + "Terminate program.");
         System.exit(0);
      }
         
      // OUTPUT
	  JOptionPane.showMessageDialog(null, "The answer to " + firstNumber + " " 
         + operatorC + " " + secondNumber + " is " + total);
         
   }
}