Objective-C 程序设计（第六版）第十章习题答案

1.

- (id) init
{
    return [self initWithWidth: 0 andHeight: 0];
}

- (id) initWithWidth: (int) w andHeight: (int) h
{
    self = [super init];
    if (self) {
        [self setWidth: w andHeight: h];
    }
    return self;
}

2.

- (id)init
{
    return [self initWithSide:0];
}

- (id) initWithSide: (int) side
{
    self = [super init];
    if (self) {
        [self setSide:side];
    }
    return self;
}

3.

//.m文件定义静态变量  增加类方法
#import "Fraction.h"

static int gCounter;

@implementation Fraction
@synthesize numerator, denominator;


- (Fraction *) add: (Fraction *) f
{
    Fraction *result = [[Fraction alloc] init];
    
   result.numerator = numerator * f.denominator + denominator * f.numerator;
   result.denominator = denominator * f.denominator;
    
    [result reduce];
    gCounter++;
    return result;
}

+ (int) count
{
    return gCounter;
}

4.

 typedef enum {Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday} Day;

5. 枚举类型不知道怎么用

        typedef Fraction * FractionObj;
        
        FractionObj f1 = [[Fraction alloc] init],
                    f2 = [[Fraction alloc] init];
        
        [f1 setTo: 1 over: 2];
        [f2 setTo: 2 over: 3];
        
        [f1 print];
        [f2 print];

6.略.