/* Calculate2.java provides a simple 5-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;

class Calculate2 extends Object
{
	static Screen theScreen = new Screen();
	static Keyboard theKeyboard = new Keyboard();

	static final String MENU = "\nPlease enter:\n" +
                      	"\ta, to perform addition;\n" +
	              		"\tb, to perform subtraction;\n" +
                      	"\tc, to perform multiplication;\n" +
                      	"\td, to perform division;\n" +
                      	"\te, to perform exponentiation;\n" +
                      	"--> ";

	public static void main(String args[])
	{

		double op1 = 0.0, op2 = 0.0;

		theScreen.println("\nWelcome to the 5-function calculator!\n");
		char operation = getMenuChoice(MENU);

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

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

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

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

		theScreen.println("\nThe result is " + result);
	}
	
	private static char getMenuChoice(String menu)
	{
		theScreen.print(menu);
		char choice;
		choice = theKeyboard.readChar();
		return choice;
	}

	private static double apply(char operation, double op1, double op2)
	{
		switch (operation)
		{
			case 'a':
				return op1 + op2;
			case 'b':
				return op1 - op2;
			case 'c':
				return op1 * op2;
			case 'd':
				return op1 / op2;
			case 'e':
//				return power(op1, (int) op2);
			default:
				theScreen.println("\nInvalid operation " + operation
						+ " received by calculator!\n");
		}
	return 0.0;
  }

// ... replace this line with the definition of power() ...

} // end of class