Question

Why it says that numerator and denominator in the category MathOps is undeclared variable ?

It is in the Chapter 11 and the Program 11.1

Can’t understand why it doesn’t work, because it is the same code as in the book without any mistakes.

Please help

Code:

    #import <Foundation/Foundation.h>  
#import "complex.h"  
#import "Fraction.h"  
#import "XYPoint.h"  

@interface Fraction (MathOps)  
-(Fraction *)add:(Fraction *) f;  
-(Fraction *)mul:(Fraction *) f;  
-(Fraction *)sub:(Fraction *) f;  
-(Fraction *)div:(Fraction *) f;  

@end  

@implementation Fraction (MathOps)  
-(Fraction *)add:(Fraction *) f  
{  
    Fraction *result = [[Fraction alloc]init];  

    result.numerator = (numerator * f.denominator)+(denominator * f.numerator);   

// numerator and denominator: Using undeclared variables.  

    result.denominator = denominator * f.denominator;  
}  
-(Fraction *)mul:(Fraction *) f  
{  
    Fraction *result = [[Fraction alloc]init];  
    result.numerator = numerator * f.numerator;  
    result.denominator = denominator * f.denominator;  

    // numerator and denominator: Using undeclared variables.  
}  
-(Fraction *)sub:(Fraction *) f {}  
-(Fraction *)div:(Fraction *) f {}  
@end  

typedef Fraction *FractionObj;  
int main (int argc, const char * argv[])  
{  

    @autoreleasepool {  
        complex *imaginary= [[complex alloc]init];  
        complex *real = [[complex alloc]init];  
        complex *results;  

        [real setReal:1];  
        [real setImaginary:2];  
        [real print];  

        [imaginary setReal:2];  
        [imaginary setImaginary:1];  
        [imaginary print];  

        results = [real add: imaginary];  
        [results print];  
        NSLog(@"FRACTIONS!");  
        Fraction *a = [[Fraction alloc]init];  
        Fraction *b = [[Fraction alloc]init];  
        id resultFraction;  

        [a setTo:20 over:3];  
        [b setTo:1 over:3];  
        [b minusSign];  
        [a minusSign];  

        id ab = a;  
        id ba = b;  
        [ab print: 0];  
        NSLog(@"-");  
        [ba print: 0];  
        NSLog(@"=");  
        resultFraction = [ab multiplyN: ba];  
        [resultFraction print: 1];  

      XYPoint *xy = [[XYPoint alloc]init];  

        [xy setX:100 andY:110];  
        [xy print];  

        NSLog(@"VERIFYING \n \n \n");  
        Fraction *fraction = [[Fraction alloc]init];  
        complex *Complex = [[complex alloc]init];  
        id number = [[complex alloc]init];  

        if([fraction isMemberOfClass: [complex class]])  
            NSLog(@"Fraction is member of class complex");  
        if([Complex isMemberOfClass: [NSObject class]])  
            NSLog(@"complex is member of class NSObject");  
        if([Complex isKindOfClass: [NSObject class]])  
            NSLog(@"complex is kind of class NSObject");  
        if([fraction isKindOfClass: [Fraction class]])  
            NSLog(@"Fraction is kind of class Fraction");  
        if([fraction respondsToSelector: @selector(print)])  
           NSLog(@"Fraction respond to selector print");  
        if([Complex respondsToSelector: @selector(print)])  
           NSLog(@"Complex responds to print");  
        if([Fraction instancesRespondToSelector: @selector(print)])  
           NSLog(@"Fraction's instances respond to print");  
        if([number respondsToSelector: @selector (print)])  
           NSLog(@"number responds to print");  
        if([number isKindOfClass: [complex class]])  
           NSLog(@"number is kind of class complex");  
        if([[number class] respondsToSelector:@selector (alloc)])  
           NSLog(@"Number class responds to alloc");  

        if([a counter]!=1){ NSLog(@"%i times was invoked method multiplyN", a.counter); }  
        else { NSLog(@"Only %i time was invoked method multiplyN", a.counter);}  

        typedef enum {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday} Day;  

    }  

    return 0;  
}  

Fraction.h:

    @interface Fraction : NSObject
@property int numerator, denominator, counter;

//methods
@end

Fraction.m

@implementation
@synthesize numerator, denominator, counter;

//methods

@end

Answer 1

Try adding a self. prefix to your code:

result.numerator = (self.numerator * f.denominator)+(self.denominator * f.numerator);