Thread: Problem with subtracting a negative fraction

For some reason, I'm getting the correct result, but my negative sign is having issues. For example, if I do 1/4 - (-2/4), I get (-3/4).

Here is my minus method for subtracting fractions.

   /**
   Subtracts a fraction from another fraction.
   @param toUse, the fraction to subtract.
   @return minusFraction, the result after subtraction.
   */   
   public Fraction minus(Fraction toUse)
   {
      int newNum = ((toUse.numerator * denominator)
                     - (numerator * toUse.denominator));
      int newDen = denominator * toUse.denominator;
      Fraction minusFraction = new Fraction(newNum, newDen);
 
      return minusFraction;
   }

Here is my reduce() method, just in case...

  /**
   Reduces the fraction, if possible, to it's simplest form.
   Converts negative fractions to the form -x/y, or if -x/-y --> x/y
   */   
   private void reduce()
   {
      int lowest = Math.abs(numerator);
      int highest = Math.abs(denominator);
 
      if (lowest > highest)
      {
         int temp = highest;
         highest = lowest;
         lowest = temp;
      }
 
      while (lowest != 0)
      {
         int temp = lowest;
         lowest = highest % lowest;
         highest = temp;
      }
 
      numerator /= highest;
      denominator /= highest;
 
      if (denominator < 0)
      {
         numerator *= -1;
         denominator *= -1;
      }
   }

I only switched an operator from my previous addition method, given here as well. I think only switching the + to a - may have caused my issue.

   /**
   Adds two fractions together.
   @param toUse, the fraction to be added.
   @return plusFraction, the sum of the two fractions.
   */   
   public Fraction plus(Fraction toUse)
   {
      int newNum = ((toUse.numerator * denominator)
                     + (numerator * toUse.denominator));
      int newDen = denominator * toUse.denominator;
      Fraction plusFraction = new Fraction(newNum, newDen);
 
      return plusFraction;
   }

I think you may want to change

int newNum = ((toUse.numerator * denominator)
- (numerator * toUse.denominator));

With

int newNum = ((numerator * toUse.denominator)
- (toUse.numerator * denominator));

- Jim