Ex 11-1. My answer

[Nick Harvey]

Here is my answer to Ex 11-1. As I have been modifying the same Fraction class files as I progress through the book, I needed to move my static variable gAddCounter to the MathOps category along with the class method to retrieve the value. This is just in case other people are growing the same class files as they progress through the book and find this useful.

As always, I welcome any feedback on good programming standards and practice.

#import "Fraction.h"

@interface Fraction (MathOps)

+(int) gAddCount;

-(Fraction *) add: (Fraction *) inFraction;
-(Fraction *) subtract: (Fraction *) inFraction;
-(Fraction *) multiply: (Fraction *) inFraction;
-(Fraction *) divide: (Fraction *) inFraction;
-(Fraction *) invert;
@end

#import "Fraction+MathOps.h"

static int gAddCount;

@implementation Fraction (MathOps)

+(int) gAddCount{
  extern int gAddCount;
  return gAddCount;
}

-(Fraction *) add: (Fraction *) inFr
{
  extern int gAddCount;
  gAddCount++;
 
  Fraction *retFr = [[Fraction allocF] init];
 
  [retFr setNumerator:((numerator * [inFr denominator]) + (denominator * [inFr numerator]))];
  [retFr setDenominator:(denominator * [inFr denominator])];
 
  [retFr reduce];
 
  return retFr;
}

-(Fraction *) subtract:(Fraction *)inFr
{
  Fraction *retFr = [[Fraction allocF] init];
 
  [retFr setNumerator:((numerator * [inFr denominator]) - (denominator * [inFr numerator]))];
  [retFr setDenominator:(denominator * [inFr denominator])];
 
  [retFr reduce];
 
  return retFr;
}

-(Fraction *) multiply:(Fraction *)inFr
{
  Fraction *retFr = [[Fraction allocF] init];
 
  [retFr setNumerator:(numerator * [inFr numerator])];
  [retFr setDenominator:(denominator * [inFr denominator])];
 
  [retFr reduce];
 
  return retFr;
}

-(Fraction *) divide:(Fraction *)inFr
{
  Fraction *retFr = [[Fraction allocF] init];
 
  [retFr setNumerator:(numerator * [inFr denominator])];
  [retFr setDenominator:(denominator * [inFr numerator])];
 
  [retFr reduce];
 
  return retFr;
}

-(Fraction *) invert
{
  Fraction *retFr = [[Fraction allocF] init];
 
  [retFr setTo:denominator over:numerator]; 
  [retFr reduce];
 
  return retFr;
}

@end