Does it or doesn't it? Ex 7.4

[MarkReid]

Can someone explain to me why or why wouldn't the Fraction class I've written work with negative fractions?

I feel that this is as much knowing the math of how negative fractions are calculated as much as anything else and unfortunately I don't have much of a clue.

I wrote a test program and it seems to work with negative fractions that I've tried but again I don't know the math behind it to really know so it's all rather confusing.

Many thanks.

[pierre]

I post a message in the Chapter 11 folder "A bug in some solutions of exercises 11.2 and 11.3" that may answer your question.

[MarkReid]

Thanks for referring me to the post. I still don't really get the math aspect of it all the same. 

Anyone else care to give describing it a shot or indeed if you want to take another try at it please?

[JasonWitz]

I don't know if they question is really "does it work", i think it's more like, "does it display correctly".   Depending on what the sign was it could screw up the way it is displayed.  For example:

1/2 / -3/4 = 4/-6 without any sign checking.  You would not want to display a fraction like this.  You would want:
1/2 / -3/4 = -4/6.

The reduction method also seemed to mess with the sign although I can't give you a case off the top of my head.  I implemented a method to check the sign and fix it if necessary.  It looks like this:

Code: (Objective-C)

-(void) checkSign {
	if ( denominator < 0  && numerator > 0) {
		denominator *= -1;
		numerator *= -1;
	}
	if (denominator < 0 && numerator < 0 ) {
		denominator *= -1;
		numerator *= -1;
	}
}

Jason

[MarkReid]

Thanks Jason.