#import <Cocoa/Cocoa.h>
//#import <foundation/nsstring.h>
@interface Fraction: NSObject
{
int numerator; //定义实例变量
int denominator; //定义实例变量
}
-(void) print;//定义了名称为print的,一个没有返回值的实例方法
-(void) setNumerator:(int) n;
-(void) setDenominator:(int) d;
@end