# Objective-C question?

Discussion in 'iOS Programming' started by EdChambo, Feb 22, 2011.

1. Feb 22, 2011
Last edited: Feb 22, 2011

### EdChambo macrumors newbie

Joined:
Nov 14, 2010
#1
Hi guys i just started learning Objective-C and i just have a quick question.

heres the program:
Code:
```#import <Foundation/Foundation.h>

@interface Fraction : NSObject
{
int numerator;
int denominator;
}

-(int) numerator;
-(int) denominator;
-(void) print;
-(void) setNumerator: (int) n;
-(void) setDenominator: (int) d;

@end

@implementation Fraction

-(int) numerator
{
return numerator;
}

-(int) denominator
{
return denominator;
}

-(void) print
{
NSLog (@"%i/%i", numerator, denominator);
}

-(void) setNumerator: (int) n;
{
numerator = n;
}

-(void) setDenominator: (int) d;
{
denominator = d;
}

@end

int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

Fraction *myFraction = [Fraction new];

[myFraction setNumerator: 1];
[myFraction setDenominator: 3];

NSLog (@"The value of myFraction is: %i/%i",
[myFraction numerator], [myFraction denominator]);
[myFraction release];

[pool drain];
return 0;
}
```
(got that outa a txt book.)

and my question is: why does

Code:
```-(void) setNumerator: (int) n;
-(void) setDenominator: (int) d;
```
have to have the arguments n and d?

couldnt you just put it as :
Code:
```-(void) setNumerator;
-(void) setDenominator;
```
????

why does it need those arguments to set the fraction?

### Staff Member

Joined:
Aug 16, 2005
Location:
New England
#2
Do you know any other programing languages or is this your first? (It would help to answer the question if we know more about what is familiar to you).

B

3. ### troop231 macrumors 603

Joined:
Jan 20, 2010
#3
Um, n and d can be anything you want them to be, look at this:
Code:
```-(void) setDenominator: (int) d;
{
denominator = d;
}```
So that's why they are like that, however you could say denominator = pancakes and it'd still work as long as you declared it earlier. like this:
Code:
```-(void) setNumerator: (int) n;
-(void) setDenominator: (int) pancakes;```

### Staff Member

Joined:
Aug 16, 2005
Location:
New England
#4
If you did that, you'd have to change the implementation to

Code:
```-(void) setDenominator: (int) pancakes;
{
denominator = pancakes;
}```
No?

B

5. ### EdChambo thread starter macrumors newbie

Joined:
Nov 14, 2010
#5
my first language.

and i understand that n is just an argument and can be anything... but y do you need it atall y can u just say set denominator:3 y does there need to be the d in there? it just seems pointless?

cus ur making this d then just saying its = to the denominator.... y dont u just say setdenominator and it sets the denominator

yeh im a noob... thats y im here... so i can be not a noob

or pancakes... y do i need that... y cant it just change the denominator?

6. Feb 22, 2011
Last edited: Feb 22, 2011

### Staff Member

Joined:
Aug 16, 2005
Location:
New England
#6
It's not. It's a place holder that lets you do things like:

Code:
`[aFraction setDenominator: 4];`
It lets the computer know that it should expect an integer there and later what to do with it. (assign its value to the denominator of your fraction object).

So, the following code would not be correct because the number there is not an integer.
Code:
`[aFraction setDenominator: 4.356];`
and

Code:
`[aFraction setDenominator];`
also would not be correct since you didn't give an integer.

EDIT: Read the bit under "Method Arguments" in chapter 3 of Kochan's book since that seems to be what you are following.

B

7. Feb 22, 2011
Last edited by a moderator: Feb 22, 2011

### EdChambo thread starter macrumors newbie

Joined:
Nov 14, 2010
#7
EDIT: Read the bit under "Method Arguments" in chapter 3 of Kochan's book since that seems to be what you are following.

yeh :L its a good book. i was just confused over this cus it seems u have 2 denominator values 1 as denominator and 1 as d?

i get it ... ima bit stupid :L

how long u rekon it takes before u can wright apps for the app store?

Joined:
Jan 20, 2010
#8
Yep

9. ### chown33 macrumors 604

Joined:
Aug 9, 2009
Location:
Sailing beyond the sunset
#9
Nope.

The following works fine:
Code:
```@interface Fraction [I]...stuff left out here...[/I]
-(void) setDenominator: (int) pancakes;

@end

@implementation Fraction
[I]...stuff left out here...[/I]
-(void) setDenominator: (int) potrzebie;
{
denominator = potrzebie;
}
```
There is no requirement that the parameter names in the @interface match the parameter names in the @implementation.

It will generally make reading the code easier if you don't give senseless names to things, and use a coherent naming approach, but the compiler won't care. It's just a symbol, and the only thing the compiler needs is for it to follow the rules for naming symbols.

10. ### troop231 macrumors 603

Joined:
Jan 20, 2010
#10
Right, but I just like it that way for making the code easier to read.

### Staff Member

Joined:
Aug 16, 2005
Location:
New England
#11
Sorry for the confusion. Perhaps a poor choice of words on my part. I wasn't meaning to imply that the @interface and @implementation needed to match, but that you had to be consistent within the @implementation.

i.e.
Code:
```@implementation Fraction
-(void) setDenominator: (int) pancakes;
{
denominator = potrzebie;
}
```
wouldn't work and I meant that you would need to change potzerbie to pancakes within the implementation.

How would you phrase that properly?

B

12. ### chown33 macrumors 604

Joined:
Aug 9, 2009
Location:
Sailing beyond the sunset
#12
I'm not sure there's a simple answer.

The issue is scope, parts, and consistency within the scope of a particular part. Maybe something like "each part must be self-consistent", but that leaves "part" pretty vague. "Each method must be self-consistent", but the principle applies to more than just methods.

"Each context" is also pretty vague, and hard to pin down because contexts are hierarchical: there is a context in which instance variables are "in scope", and that context continues across all the methods within an @implementation/@end grouping. There's also a "global context" that would encompass any extern variables, class declarations, etc.

### Staff Member

Joined:
Aug 16, 2005
Location:
New England
#13
Glad it's not just me. Or maybe it still is?

B