/*	ProblemGenerator.java
*	@author: Charles Bell
*	@version: Mar 9, 2002
*	email: charbell@bellsouth.net
*
*/

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

/**	ProblemGenerator
*/
public class ProblemGenerator{

	Random random = new Random();

	/**	
	*/
	public static void main(String[] args){

		ProblemGenerator problemgenerator = new ProblemGenerator();
		problemgenerator.generate();

	}

	/**	Queries the user to  enter the number of problems to 
	*	generate, generates them, poses the problem, and prompts
	*	for an answer, displays feedback and the correct answer,
	*	if missed, and the cumulative score.
	*/
	public void generate (){

		showMessage("How many problems would you like?");
		int problems = getPositiveInteger();
		showMessage("Generating " + String.valueOf(problems) + " problems.");
		int score = 0;
		int correctresponses = 0;
		for (int i = 0; i < problems;i++){
			int first = getRandomInt(1,12);
			int second = getRandomInt(1,12);
			String question = String.valueOf(first) + " x " + 
				String.valueOf(second);
			showMessage("Question: " + question + "?");
			int useranswer = getPositiveInteger();
			int correctanswer = first * second;
			if (useranswer == correctanswer){
				showMessage("Correct!");
				correctresponses++;
			}else{
				showMessage("No, " + question  + " is " + 
					String.valueOf(correctanswer));		
			}
			showMessage(score(i+1,correctresponses));
		}
		showMessage("Your final score was " + score(problems,correctresponses));

	}

	/**	Returns a random integer between low and high, inclusive.
	*	Random.nextInt(int n) returns next random between 0 
	*	inclusive and n exclusive, so must adjust for low and high.
	*/
	public int getRandomInt(int low, int high){
		int highinclusive = high + 1;
		int n = random.nextInt(highinclusive - low);
		return low + n;		
	}

	/**	Returns a string corresponding to the percentage
	*	of a  correct answers a out of n problems.
	*/ 
	public String score(int n, int a){
		float ratio = 0f;
		if (n > 0) {
			ratio = (float) a / (float) n;
		}
		float percent = ratio * 100f;
		return String.valueOf(percent + "%");
	}

	/**	Displays message string to System.out.
	*/
	public void showMessage(String message){
		System.out.println(message);
	}

	/**	Loops until the user enters a positive integer.
	*/
	public int getPositiveInteger(){
		int n = -1;
		while (n < 0){
			String input = getUserInput();
			if (isInteger(input)){
				n = toInt(input);
			}
		}
		return n;
	}

	/**	Obtains a line of input from the user using 
	*	InputStream System.in.
	*/
	public String getUserInput(){
		String lineread = "";
		try{
			InputStreamReader isr = new InputStreamReader(System.in);
			BufferedReader br = new BufferedReader(isr);
			lineread = br.readLine();
		}catch(IOException ioe){
			System.err.println("IOException: " + ioe.getMessage());
		}
		return lineread;
	}

	/**	Converts the input string to an integer 
	*	or returns -1 if unsucessful.
	*/
	public int toInt(String s){
		int n = -1;
		try{
			n = Integer.parseInt(s);
		}catch(NumberFormatException nfe){
			System.err.println("NumberFormatException: " + nfe.getMessage());
			System.err.println(s + " can not be converted to an integer.");
		}
		return n;
	}

	/**	Returns true if the input string can be converted 
	*	to an integer. False otherwise.
	*/
	public boolean isInteger(String s){
		boolean status = false;
		try{
			int n = Integer.parseInt(s);
			//program execution will not reach next line
			//unless parse is sucessful.
			status = true;
		}catch(NumberFormatException nfe){
			status = false;
		}
		return status;
	}	
}