代码清单3-3 ,objective-C

#import <Foundation/Foundation.h>


//---- @interface ---
@interface Fraction: NSObject

-(void) print;
-(void) setNumerator: (int) n;
-(void) setDenominator: (int) d;

@end

//---- @implementation block ---
@implementation Fraction
{
    int numerator;
    int denominator;
}

-(void) print {
    NSLog(@"%i/%i", numerator, denominator);
}

-(void) setNumerator:(int)n {
    numerator = n;
}

-(void) setDenominator:(int)d {
    denominator = d;
}

@end


int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        
        //分数调用部分，分数类，只能写在前面与c语言类似。
        Fraction *frac1 = [[Fraction alloc] init];
        Fraction *frac2 = [[Fraction alloc] init];
        
        [frac1 setNumerator: 2];
        [frac1 setDenominator: 3];
        
        [frac2 setNumerator: 3];
        [frac2 setDenominator: 7];
        
        NSLog(@"First fraction is:");
        [frac1 print];
        
        NSLog(@"Second fraction is:");
        [frac2 print];
    }
    return 0;
}