基类接口文件

1. 
   
2. #import <Foundation/Foundation.h>
   
3. 
   
4. @interface Fraction : NSObject
   
5. 
   
6. @property (nonatomic ) int numerator,denominator;
   
7. 
   
8. -(void)setTo:(int) n over:(int) d;
   
9. 
   
10. -(void)reduce;//约分
    
11. -(NSString *)description;//显示方法重写
    
12. 
    
13. 
    
14. @end
    

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基类的实现文件

1. 
   
2. #import "Fraction.h"
   
3. 
   
4. @implementation Fraction
   
5. 
   
6. @synthesize  numerator,denominator;
   
7. 
   
8. -(void)setTo:(int) n over:(int) d
   
9. {
   
10.     numerator =n;
    
11.     denominator=d;
    
12. }
    
13. -(void)reduce
    
14. {
    
15.     int u=numerator;
    
16.     int v=denominator;
    
17.     int temp;
    
18.    
    
19.     while (v!=0)
    
20.     {
    
21.         temp=u%v;
    
22.         u=v;
    
23.         v=temp;
    
24.     }
    
25.     numerator/=u;
    
26.     denominator/=u;
    
27. }
    
28. 
    
29. -(NSString *)description
    
30. {
    
31.     [self reduce];
    
32.     return [NSString stringWithFormat:@"%d/%d",numerator,denominator];
    
33. }
    
34. @end
    

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为其添加分类单独放在一个文件中

1. 
   
2. #import "Fraction.h"
   
3. 
   
4. //实现Fraction的分类
   
5. @interface Fraction (MathOps)
   
6. 
   
7. //+
   
8. -(Fraction *)add:(Fraction *)f;
   
9. //X
   
10. -(Fraction *)mul:(Fraction *)f;
    
11. //-
    
12. -(Fraction *)sub:(Fraction *)f;
    
13. //约分
    
14. -(Fraction *)div:(Fraction *)f;
    
15. 
    
16. @end
    
17. 
    
18. 
    
19. //实现部分
    
20. @implementation Fraction (MathOps)
    
21. 
    
22. 
    
23. //将两个分数相加
    
24. //a/b+c/d=(a*d)+(b*C)/db
    
25. -(Fraction *)add:(Fraction *)f
    
26. {
    
27.     //定义临时变量
    
28.     Fraction *result=[Fraction new];
    
29.    
    
30.     result.numerator=numerato*f.denominator)+(denominator*f.numerator);
    
31.     result.denominator=denominator*f.denominator;
    
32.    
    
33.     [result reduce];
    
34.    
    
35.     return result;
    
36.    
    
37. }
    
38. //X
    
39. -(Fraction *)mul:(Fraction *)f
    
40. {
    
41.    
    
42. }
    
43. //-
    
44. -(Fraction *)sub:(Fraction *)f
    
45. {
    
46.    
    
47. }
    
48. //约分
    
49. -(Fraction *)div:(Fraction *)f
    
50. {
    
51.    
    
52. }
    
53. @end

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问题：为啥分类中    result.numerator=numerato*f.denominator)+(denominator*f.numerator);的出现use of undeclared identifier提示，我不是已经包含基类.h文件了吗？

我明白了，我把定义合成方法时numerator和调用使用不使用self记混了，加上self即可

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

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