/* Calculate.java provides a simple 4-function calculator.
 *
 * Adapted by: Charles Hoot, for Hands On Java.
 * From: Joel Adams, for Hands On C++.
 * Completed by:
 * Date:
 * Purpose:
 *
 * Specification:
 * input(keyboard): a char, stored in operator;
 *                  two reals, stored in op1 and op2;
 * output(screen): the result of the expression (op1 operator op2).
 *****************************************************************/

import ann.easyio.*;
import hoj.Assertion;

public class Calculate extends Object
{
  static Screen theScreen = new Screen();
  static Keyboard theKeyboard = new Keyboard();

  static final String MENU = "\nPlease enter:\n" +
                      	"\t+, to perform addition;\n" +
	              		"\t-, to perform subtraction;\n" +
                      	"\t*, to perform multiplication;\n" +
                      	"\t/, to perform division;\n" +
                      	"--> ";

  public static void main(String args[])
  {
  	theScreen.println("\nWelcome to the 4-function calculator!\n" + MENU);
  	char operation;

	operation = theKeyboard.readChar();
  	Assertion.check(operation == '+' || operation == '-' ||
          		operation == '*' || operation == '/');

	theScreen.print("\nNow enter your operands: ");

	double op1, op2;
	op1 = theKeyboard.readDouble();
	op2 = theKeyboard.readDouble();

	Assertion.check(operation != '/' || op2 != 0);

	double result = apply(operation, op1, op2);

	theScreen.println("\n" + op1 + operation + op2
       + " = " + result);
  }

  // ... Replace this line with the definition of apply()

}