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Author Topic: Allocating and returning Objects from Methods HeLp!  (Read 1681 times)
macifone
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« on: November 05, 2009, 02:57:24 PM »

I have trouble on the bottom of page 150 where it starts talking about, like the title says, allocating and returning objects.
So I get that a new object called result is being made, why is resultNum and resultDenom being made?

Dosnt result fraction object already have its own members (instance vars) of numerator and denominator?

Or am I missing something?

Back on page 144 where it starts the add: method I think I got confused with where it says

numerator1 = numerator * f.denominator
                       ...
denominator1 = denominator * f.denominator

Isnt numerator1 and denominator1 (i just put 1  after it to tell difference) instance vars of what?
I am so confused.
I have no idea what anyhting is.
PLEASEE HELPPP MEEEEE!





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skochan
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« Reply #1 on: November 05, 2009, 03:18:35 PM »

resultNum and resultDenom are just temporary variables used to hold the result of calculating the numerator and denominator, respectively, of the result of the addition of the two fractions.  The values in these two variables are then used to set the numerator and denominator of the result fraction with the subsequent setTo:over: method call.

When numerator and denominator are used by themselves in the method, they refer to the corresponding instance variables of the Fraction object that got sent the add: message (i.e, the message receiver).   Remember, that's always the case:  you can reference the receiver's instance variables directly by name.  On the other hand, the expressions f.numerator and f.denominator are used to reference the numerator and denominator, respectively, of the argument to the add: method (which we call f).

Hope this helps.

Cheers,

Steve Kochan
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macifone
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« Reply #2 on: November 05, 2009, 03:34:45 PM »

Thanks now I get it, also because its returning result the add: method has a return typr of fraction?
On page 151 and 152, why is the object resultFraction made couldnt the program 7.5 work without that?
Cause all it does is store the output of [aFraction add: bFraction];
and then prints it.
Thanks for helping.
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skochan
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« Reply #3 on: November 05, 2009, 08:20:25 PM »

It's stored so it can be released later.  Read the sticky at the top of this topic.

Cheers,

Steve Kochan
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