objective-c - 在Objective-C中出现类别问题

Question

我正在做一些练习，但不明白哪里出了问题。

我有:

分数+ MathOps.h

#import "Fraction.h"

@interface Fraction (MathOps)
-(Fraction *) add:(Fraction *) f;
@end

这是Fraction + MathOps.m

#import "Fraction+MathOps.h"

@implementation Fraction (MathOps)

-(Fraction *) add:(Fraction *) f
{
    //To add two fraction
    // a / b + c / d = ((a * b) + (b * c)) / (b * d)

    Fraction *result = [[Fraction alloc] init];

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

    [result reduce];

    return result;
}

@end

并尝试从main.m中的类别调用方法add

Fraction *ca = [[Fraction alloc] init];
Fraction *cb = [[Fraction alloc] init];
Fraction *cresult;

[ca setTo: 1 over: 3];  
[cb setTo: 2 over: 5];  

cresult = [ca add: cb];

并出现编译器错误(“Fraction”没有可见的@interface声明选择器“add:”
)at cresult = [ca add:cb]字符串。

Answer 1

已解决的问题:
我没有在main.m中包含Fraction + MathOps.h
谢谢理查德和卡尔·诺鲁