Defining a Class in Objective C, XCode

Question

Hello;

I am new to Objective C, and am trying to write a class that defines a complex number. The code seems fine but when I print to the console, my values for instance variables are 0.

Here is the code:

//
//  ComplexNumber.h
//  Mandelbrot Set
//
//  Created by Brett on 10-06-02.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <stdio.h>


@interface ComplexNumber : NSObject {

 double real;
 double imaginary;

}

// Getters
-(double) real;
-(double) imaginary;



// Setters
-(void)setReal: (double) a andImaginary: (double) b;

//Function
-(ComplexNumber *)squared;

@end


//
//  ComplexNumber.m
//  Mandelbrot Set
//
//  Created by Brett on 10-06-02.
//  Copyright 2010 __MyCompanyName__. All rights reserved.
//

#import "ComplexNumber.h"
#import <math.h>
#import <stdio.h>

@implementation ComplexNumber

-(double)real{
 return self->real;
}

-(double)imaginary{
 return self->imaginary;
}


-(void)setReal: (double) a andImaginary: (double) b{

 self->real=a;
 self->imaginary=b;

}

-(ComplexNumber *)squared{

 double a = pow(real,2);
 double b = pow(imaginary, 2);
 double c = 2*real*imaginary;

 ComplexNumber *d;
 [d setReal:(a-b) andImaginary: c];

 return d;
}

@end

In the App Delegate for debugging purposes I added:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {   

 ComplexNumber *testNumber = [[ComplexNumber alloc] init];
 [testNumber setReal:55.0 andImaginary:30.0];
 NSLog(@"%d", testNumber.real);

    // Override point for customization after app launch    
    [window addSubview:viewController.view];
    [window makeKeyAndVisible];

 return YES;
}

But the console returns 0 everytime. Help?

Answer 1

Instead of %d, use %f. D is for integers, F is for floating point ("real").

Answer 2

The problem is that you don't allocate the return value of your -(ComplexNumber *)squared method.

You do it correctly when you create testNumber. You have..

ComplexNumber *d;

and

ComplexNumber *testNumber = [[ComplexNumber alloc] init];

they should follow the same pattern (It's the general pattern for creating a new instance of an object).

You might want to define a custom initializer:-

- (id)initWithReal:(double)a andImaginary:(double)b { 
  self = [super init];
  if(self){
    real = a;
    imaginary = b;
  }
  return self;
}

and then instead of

ComplexNumber *testNumber = [[ComplexNumber alloc] init];
[testNumber setReal:55.0 andImaginary:30.0];

You could use

ComplexNumber *testNumber = [[ComplexNumber alloc] initWithReal:55.0 andImaginary:30.0];

As a sidenote:

self->real=a; is the same as real=a. As there is no need for -> you should not use it. If you need to access the variables from another onject you use the getter and setter methods.

Oh yeah, and as the other have pointed out. The format specifier in the NSLog is wrong as well.

Answer 3

A couple things. In your getters/setters why are you using self->real specifically the -> syntax. I've only seen/used self.real. You way may work (?) but the convention is to use a peroid. Also why are you manually creating the geters/seters. Unless you need to do more logic then just return and assign in them I'd suggest changing to this.

//.h
#import <Foundation/Foundation.h>
#import <stdio.h>

@interface ComplexNumber : NSObject {

      double real;
      double imaginary;
}
   @property (nonatomic) double real;
   @property (nonatomic) double imaginary;

   //Function
   -(ComplexNumber *)squared;
@end



//.m
#import "ComplexNumber.h"
#import <math.h>
#import <stdio.h>

@implementation ComplexNumber

-(ComplexNumber *)squared{

 double a = pow(real,2);
 double b = pow(imaginary, 2);
 double c = 2*real*imaginary;

 ComplexNumber *d = [[ComplexNumber alloc] init];
 d.real = a-b;
 d.imaginary = c;
 return d;
}

@end

Let objective-c create your basic getters/setters for you via the @property line. You can then access/set them the following ways.

ComplexNumber *d = [[ComplexNumber alloc] init];
d.real = 55; //or
[d setReal:55];
//with reading as easy
double real = d.real; //or
double real = [d real];