// **** Imports ****
import java.io.*;
import java.util.*;

/** 
 * Class: TrivialExample3.
 * <br>Description: This trivial examples illustrates how to use
 * the  buildFromInfix and evaluate methods in the ExprEvaluator
 * class.  This example uses the getValueOf(var, value), setValueOf(var),
 * and evaluate() methods.  
 * <p>
 * The techniques in this example are useful
 * when only a few variables are used.  See TrivailExample2 for a class using
 * evaluate(var) where var is an array of values for all 26 variables.  
 * TrivialExample uses techniques suitable when only the "common" variables
 * t, x, and y are used.
 * 
 *<p>
 * To evaluate prefix or postfix expressions, simply replace "buildFromInfix" by
 * "buildFromPrefix" or "buildFromPostfix".
 * <p>
 * <b>Requires:</b>
 * <br>ExprEvaluator.java
 * <br>EasyFormat.java
 * <br>DoubleScanner.java
 * @version Date: 6/10/2008
 * @author James Brink, brinkje@plu.edu
 */
public class TrivialExample3 {

   double valA, valX, valY;
   double infixVal;
   String infix;
   ExprEvaluator evaluator = new ExprEvaluator();
   Scanner scan = new Scanner(System.in);

   /**
    * Constructor for TrivialExample3.
    *
    * Note:  in this case, the expression only uses variables a, x and y.  The
    * values are passed one at time using setValueOf and then the 0 parameter 
    * version of evaluate is used.
    */
   public TrivialExample3() {
      // get input
      System.out.print("Enter the value for a: ");
      valA = scan.nextDouble();
      System.out.print("Enter the value for x: ");
      valX = scan.nextDouble();
      System.out.print("Enter the value for y: ");
      valY = scan.nextDouble();
      scan.nextLine();   //  read rest of line
      System.out.print("Enter the expression to be evaluated: ");
      infix = scan.nextLine();

      // evaluate expression and print the results
      try {
         evaluator.setValueOf('a', valA);
         evaluator.setValueOf('x', valX);
         evaluator.setValueOf('y', valY);
         evaluator.buildFromInfix(infix);
         System.out.println("The results are");
         infixVal = evaluator.evaluate();
         System.out.println("a = " + evaluator.getValueOf('a')
                                   + ", x = " +  evaluator.getValueOf('x')
                                   + ", y = " +  evaluator.getValueOf('y')
                                   + ", expression = " + infixVal);
      }catch (Exception e) {
         System.out.println ("Error:  namely: " + e);
      }
   }  // constructor TrivialExample3

   /**
    * Trivial main program that starts the application.
    */
   public static void main (String args[]) {
      TrivialExample3 app = new TrivialExample3();
      System.exit(0);
   }  // end main

} // class TrivialExample3