import java.io.*;
import java.util.*;

/** 
 * Class: TrivialExample2.
 * <br>Description: This trivial examples illustrates how to use
 * the  buildFromInfix and evaluate methods in the ExprEvaluator
 * class.  This example uses evaluate(vars) where vars is an array 
 * of values for all 26 variables. 
 * <p>
 * The techniques in this example may be 
 * useful when several variables are used.  See Trivial Example3 for an
 * example using the getValueOf(var, value), setValueOf(var),
 * and evaluate() methods.  
 * 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 TrivialExample2 {

   double [] vars = new double[26]; // all values set to 0 initially
   double infixVal;
   String infix;
   ExprEvaluator evaluator = new ExprEvaluator();
   Scanner scan = new Scanner(System.in);

   /**
    * Constructor for TrivialExample2.
    *
    * Note:  in this case, the expression uses variables a, x and y.  The 
    * values of the variables are stored in an array "vars" which is 
    * passed by an evaluate method.
    */
   public TrivialExample2() {
      // get input
      System.out.print("Enter the value for a: ");
      vars['a' - 'a'] = scan.nextDouble();
      System.out.print("Enter the value for x: ");
      vars['x' - 'a'] = scan.nextDouble();
      System.out.print("Enter the value for y: ");
      vars['y' - 'a'] = 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.buildFromInfix(infix);
         System.out.println("The results are");
         infixVal = evaluator.evaluate(vars);
         // // variable values may have changed so use evaluator.getValueOf
         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 TrivialExample2

   /**
    * Trivial main program that starts the application.
    */
   public static void main (String args[]) {
      TrivialExample2 app = new TrivialExample2();
      System.exit(0);
   }  // end main

} // class TrivialExample2