Thread: Rational - GCD issue

Hello, I am having trouble trying to build the "gcd(Greatest common divisor". It's where if I input "1/2 - 3/4" output would be "-2/8", where I would want "-1/4". Here is my code. I finished all my arithmetic's, and now all I need to do is simplify my answers. After that, I should be good with this code. Any help is appreciated.

import java.util.Scanner;
 
 
public class Rational {
 
 
  // TODO Auto-generated method stub
  //Data members
   private int numerator;
   private int denominator;
  //Constructors
  Rational()
  { 
 
   numerator = 0;
   denominator = 1;
  }
 
  Rational(int num, int den)
  {
 
   numerator = num;
   denominator = den;
  }
 //Accessors
  public int getNumerator()
  {
   return numerator;
  }
  public int getDenominator()
  {
   return denominator;
  }
  // Modifiers
  public void setNumerator(int num)
  {
   numerator = num;
  }
  public void setDenominator(int den)
  {
   denominator = den;
  }
  public Rational inputRational(){
  Scanner input = new Scanner(System.in);
  System.out.println("Enter numerator");
  numerator = input.nextInt();
  System.out.println("Enter Denominator");
  denominator = input.nextInt();
  return new Rational(numerator, denominator);
 
 }
 public String toString()
 {
  return numerator + "/" + denominator;
 }
 private static int gcd(int m, int n)
    {
        int r;
        while(n!= 0)
        {
            r = m % n;
            m = n;
            n = r;     
            }
        return m;
        }
 
 //Adding
 public Rational add(Rational f)
 {
  int num;
  int den;
  num = (numerator * f.denominator) + (f.numerator * denominator);
  den = denominator * f.denominator;
  return new Rational(num, den);
 }
 public void sub(Rational f1, Rational f2)
 {
  numerator = (f1.numerator * f2.denominator) - (f2.numerator * f1.denominator);
  denominator = f1.denominator * f2.denominator;
 
 }
 public Rational mul(Rational f)
 {
  int num;
  int den;
  num = numerator * f.numerator;
  den = denominator * f.denominator;
  return new Rational(num, den);
 }
 public void div(Rational f1, Rational f2)
 {
  this.numerator = f1.numerator * f2.denominator;
  this.denominator = f1.denominator * f2.numerator;
 }
 public static double divided(Rational f1, Rational f2)
 {
  double value;
  value = (f1.numerator/f2.denominator)*(f2.denominator/f2.numerator);
  return value;
  }
 }

Here's my tester.

public class TestRational {
 
 public static void main(String[] args) {
  // TODO Auto-generated method stub
  Rational f1 = new Rational();
  Rational f2 = new Rational();
  Rational f3 = new Rational();
  f1.inputRational();
  f2.inputRational();
 
  f3 = f1.add(f2);
  System.out.println(f1.toString() + " + " + f2.toString() + " = " + f3.toString());
 
  f3.sub(f1,f2);
  System.out.println(f1.toString() + " - " + f2.toString() + " = " + f3.toString());
 
  f3 = f1.mul(f2);
  System.out.println(f1.toString() + " * " + f2.toString() + " = " + f3.toString());
 
  f3.div(f1, f2);
  System.out.println(f1.toString() + " / " + f2.toString() + " = " + f3.toString());
 
  System.out.println(Rational.divided(f1,f2));
  f1.setNumerator(2);
  f2.setDenominator(5);
  System.out.println("Numerator: " +f1.getNumerator());
  System.out.println("Denominator: "+f2.getDenominator());
 }
 
}

This is a time when posting an example run would be helpful to explain what you're asking for help with. So when I run your code for the fractions you suggest, I get:

Enter numerator
1
Enter Denominator
2
Enter numerator
3
Enter Denominator
4
1/2 + 3/4 = 10/8
1/2 - 3/4 = -2/8
1/2 * 3/4 = 3/8
1/2 / 3/4 = 4/6
0.0
Numerator: 2
Denominator: 5

Are you asking for help to simplify all of the resulting fractions, 10/8, -2/8, 3/8, and 4/6?

What are the results 0.0, Numerator: 2 and Denominator: 5 supposed to be? Are those right?

I notice that you never use the method gcd(). Why is that?

Originally Posted by GregBrannon

This is a time when posting an example run would be helpful to explain what you're asking for help with. So when I run your code for the fractions you suggest, I get:

Enter numerator
1
Enter Denominator
2
Enter numerator
3
Enter Denominator
4
1/2 + 3/4 = 10/8
1/2 - 3/4 = -2/8
1/2 * 3/4 = 3/8
1/2 / 3/4 = 4/6
0.0
Numerator: 2
Denominator: 5

Are you asking for help to simplify all of the resulting fractions, 10/8, -2/8, 3/8, and 4/6?

What are the results 0.0, Numerator: 2 and Denominator: 5 supposed to be? Are those right?

I notice that you never use the method gcd(). Why is that?

Thanks for the reply. Yes, I was missing the method gcd. Here is what i've done.

int divisor = gcd(numerator, denominator);
numerator = numerator/divisor;
denominator = denominator/divisor;

^this should be posted right after the add/sub/mul/div parts. It works for Sub/Div.

if (numerator == 0){
return "0";
}
else if (numerator == denominator){
return "1";

^I put this in the ToString method. So, yeah, just figuring out whats wrong with simplifying the addition & Multiplication, and i'm finish with this work.

Hello.
You are still fine.
Suppose your output is n/m. You can find the common factors for n and m one by one. If a factor say 'f' is found then reduce both n and m by f. With this you can avoid GCD.

Syed.