实现Square类，让其继承自Rectangle类，并在Square类增添新属性和方法

#import <Foundation/Foundation.h>

@interface Rectangle : NSObject{
    int width;
    int height;
}
@property int width,height;
-(int) area;
-(int) perimeter;
-(void)setWidth:(int)w andHeight:(int)h;

@end


#import "Rectangle.h"

@implementation Rectangle
@synthesize width,height;
-(void)setWidth:(int)w andHeight:(int) h{
    width=w;
    height=h;
}
-(int) area{
    return width*height;
}
-(int) perimeter{
    return (width+height)*2;
}

@end



#import <Foundation/Foundation.h>
#import "Rectangle.h"
@interface Square : Rectangle
-(void) setSide:(int) s;
-(int)side;
-(int)area;
-(int)perimeter;

@end


#import "Square.h"

@implementation Square

-(void) setSide:(int) s{
    [self setWidth:s andHeight:s];
}

-(int) side{
    return width;
}

-(int)area{
    return width*width;
}

-(int)perimeter{
    return 2*(width+height);
}
@end