package chapter2;

import java.util.Random;
import java.util.Scanner;

public class ElementaryMath 
{
	public static void main(String[] args)
	{
		Random rng = new Random();
		Scanner in = new Scanner(System.in);

		//choose question type
		int MULT = 1; //create constants
		int DIVIDE = 2;
		int ADD = 3;
		int SUB = 4;

		int questionType = 0;
		
		while (questionType< MULT || questionType > SUB)
		{
			System.out.println("Choose type of problem: \n1 for multipliation, \n2 for division, \n" +
					"3 for addition,  \n4 for subtraction");
			if (in.hasNextInt())
				questionType = in.nextInt();
			else
				in.nextLine();
		}
		
		//print instructions for division
		if (questionType == DIVIDE)
		{
			System.out.println("Please give your answer as quotient R remainder.  " +
					"For example if the question is 13/5, enter: 2 R 3 ");
		}
		
		//ask 10 questions
		for (int i=0; i<10; i++) //each question
		{
			int num1 = rng.nextInt(10);
			int num2 = rng.nextInt(10);
			
			if (questionType == DIVIDE)
			{
				if (num2 == 0)
					num2++;
				int quotient = num1 / num2; //integer division
				int remainder = num1 % num2; 
				String answer = "";
				
				System.out.printf("%d / %d = ", num1, num2);
				do 
				{
					answer = in.nextLine();
				}while (answer.length() == 0);
				
				//assume good input for now
				String studentQ = answer.trim().substring(0,1); //first character as a string;
				int studentQuotient = Integer.parseInt(studentQ);
				int studentRemainder = Integer.parseInt(answer.substring(answer.length()-1));
				
				if (studentQuotient == quotient && studentRemainder == remainder)
					System.out.println("  Correct");
				else
					System.out.println("  I'm sorry, that is incorrect.");	
			}
			else //add, subtract, and multiply have just one answer
			{
				int correctAnswer;
				if (questionType == MULT)
				{
					correctAnswer = num1 * num2;
					System.out.printf("%d times %d = ", num1, num2);
				}
				else if(questionType == ADD)
				{
					correctAnswer = num1 + num2;
					System.out.printf("%d plus %d = ", num1, num2);
				}
				else  //must be subtraction
				{
					correctAnswer = num1 - num2;
					System.out.printf("%d minus %d = ", num1, num2);
				}
					
				int studentAnswer = correctAnswer - 1;//initialize to wrong answer
			
				do
				{					
					if( in.hasNextInt() )
						studentAnswer = in.nextInt();
					else
						in.nextLine();
					if (studentAnswer != correctAnswer)
						System.out.printf("  Incorrect. Please try again: " );
					
				}//end do
				while(studentAnswer != correctAnswer);
					
				System.out.println("  Correct.\n");	
			}//end add, sub, mult if statement			
		}//end for
		
		System.out.println("Well done.  This lesson is complete.");
	}//end main
}//end class