CS302 Fall 2012 Exam 2 Solution

// Part III: Write an Instantiable Class
import java.util.Random;
public class ProblemGen {

  public static final int ADD = 0;
  public static final int SUB = 1;
  public static final int MUL = 2;
  public static final int DIV = 3;

  private final int MIN; // 
  private final int MAX; // 
  private final int OP;  // 

  private int op1, op2;     // the operands
  private String question;  // the problem
  private double answer;    // the answer

  private static Random rng = new Random();

  public ProblemGen (int low, int hi, int op) {
    MIN = low; MAX = hi; OP = op; 
    nextQuestion();
  }
  private void nextQuestion() {
    op1 = rng.nextInt(MAX-MIN+1)+MIN; // randomly pick each operand
    op2 = rng.nextInt(MAX-MIN+1)+MIN;
    // set question and answer fields
    char c = '?'; answer = 0; 
    if ( OP == ADD )      { c = '+'; answer = op1 + op2; } 
    else if ( OP == SUB ) { c = '-'; answer = op1 - op2; } 
    else if ( OP == MUL ) { c = '*'; answer = op1 * op2; } 
    else if ( OP == DIV ) { c = '/'; answer = op1 / (double)op2; } 
    question = op1 + " " + c + " " + op2 ;
  }

  public String getQuestion() { return question; }
  public String toString()    { return question + " = " + answer; } 

  public boolean isCorrect( double possible ) {
    double err = 0.001; // returns true if possible is close to answer
    return ( answer-err < possible && possible < answer+err );
  }