// Exercise 4.11 Solution: Gas.java
// Program calculates average mpg

// Java core packages
import java.text.DecimalFormat;

// Java extension packages
import javax.swing.JOptionPane;

public class Gas {

   // main method begins execution of Java application
   public static void main( String args[] )
   {
      int miles, gallons, totalMiles = 0, totalGallons = 0;
      float milesPerGallon, totalMilesPerGallon;
      String inputMiles, inputGallons, result = "";

      // read first number from user as a string
      inputMiles = JOptionPane.showInputDialog(
         "Enter miles (-1 to quit):" );

      // convert miles from type String to type int
      miles = Integer.parseInt( inputMiles );

      // exit if the input is equal to -1
      // otherwise, proceed with the program
      while ( miles != -1 ) {
         // read second number from user as String
         inputGallons = JOptionPane.showInputDialog(
            "Enter gallons:" );

         // convert gallons from type String to type int
         gallons = Integer.parseInt( inputGallons );

         totalMiles += miles;
         totalGallons += gallons;

         DecimalFormat twoDigits = new DecimalFormat( "0.00" );

         if ( gallons != 0 ) {
            milesPerGallon = (float) miles / gallons;
            result = "MPG this tankful: " +
               twoDigits.format( milesPerGallon ) + "\n";
         }

         totalMilesPerGallon = (float) totalMiles / totalGallons;
         result += "Total MPG: " +
            twoDigits.format( totalMilesPerGallon ) + "\n";

         JOptionPane.showMessageDialog( null, result, "Milage",
            JOptionPane.INFORMATION_MESSAGE );

      	 // input new value for miles and
      	 // convert from String to int
      	 inputMiles = JOptionPane.showInputDialog(
            "Enter miles (-1 to quit):" );
         miles = Integer.parseInt( inputMiles );
      }  // end while loop


      System.exit( 0 );

   }  // end method main

}  // end class Gas