Question

为什么它表示 MathOps 类别中的分子和分母是未声明的变量？

位于第11章和计划11.1

无法理解为什么它不起作用，因为它与书中的代码完全没有任何错误。

请帮忙

代码：

    #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

你可能想检查你的Fraction类文件.h，检查你是否有一个分子和分母的set属性。

@property(nonatomic, ...) Type *numerator
@property(nonatomic, ...) Type *denominator

以及.m文件中应该有

@synthesize numerator, denominator

或者，在您的xcode中，将鼠标指向该分子或分母，同时按住Command键然后单击该变量，xcode将带您到声明变量的文件，如果未声明，则不会发生任何事情。

Answer 2

尝试在代码中添加self.前缀：

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

Answer 3

看起来您没有使用任何先前设置的变量来使用分子和分母。您可能会对这些变量与其他变量具有相同名称这一事实感到困惑，但如果它们与从中调用的文件没有关联，那么您的程序将无法识别它们。您的Synthesis语句可能需要移动到@implementation语句下面。我对你所展示的代码不包含分子和分母的声明这一事实感到有些困惑，我确信你的编译器也是如此。

没有使用书中的相同代码＆lt;＆＃34; Programming Objective-c 4th edition＆＃34; Stephen Kochan＆gt;

3 个答案: