用继承实现XYPoint和Circle两个类

#import <Foundation/Foundation.h>
@protocol show
@required
-(void)printOn;
@end

@interface XYPoint : NSObject<show>{
    int x;
    int y;
}
@property (nonatomic,assign)int x,y;
-(id)setX:(int)_x andY:(int)_y;

@end

#import "XYPoint.h"

@implementation XYPoint
@synthesize x,y;

-(id)setX:(int)_x andY:(int)_y{
    self.x=_x;
    self.y=_y;
    return self;
}
-(void)printOn{
    NSLog(@"x = %d ,y = %d",x,y);
}
@end

#import <Foundation/Foundation.h>

#import "XYPoint.h"
@interface Circle : XYPoint<show>{
    int radius;
}
@property (nonatomic,assign)int radius;
-(id)initWithX:(int)_x andY:(int)_y andRadius:(int)_r;
-(double)area;
-(double)perimeter;
@end

#import "Circle.h"

@implementation Circle
@synthesize radius;
-(id)initWithX:(int)_x andY:(int)_y andRadius:(int)_r;
{
    self.x=_x;
    self.y=_y;
    self.radius=_r;
    return self;
}

-(double)area{
    return 3.14*radius*radius;
}

-(double)perimeter{
    return 2*3,14*radius;
}

-(void)printOn{
    NSLog(@"x = %d, y = %d ,radius = %d",x,y,radius);
    
}
@end