//
//  main.m
//  OC-特殊数据类型
//
//  Created by wangtouwang on 15/3/20.
//  Copyright (c) 2015年 wangtouwang. All rights reserved.
//

#import <Foundation/Foundation.h>
#import "Person.h"int main(int argc, const char * argv[]) {@autoreleasepool {// 首先介绍nil 代表对象空指针Person  *p = [Person new];NSLog(@"%@",p==nil?@"TRUE":@"FALSE");Person *p2 ;NSLog(@"%@",p2==nil?@"TRUE":@"FALSE");Class pc = [Person class];// 介绍 Nil 代表类是否存在NSLog(@"%@",pc==Nil?@"TRUE":@"FALSE");Class testClass ;NSLog(@"%@",testClass==Nil?@"TRUE":@"FALSE");//介绍 NULL NULL 是个值  对Objective-C值类型为空：int number = Null;(相当于 int number = 0;)  ( #define NULL ((void *)0)  )int *money=NULL;if (money == 0 )NSLog(@"money is NULL");elseNSLog(@"money is not NULL");//介绍 NSNull 空对象 主要是适用于 数组  因为在NSArray和NSDictionary中nil中有特殊的含义（表示列表结束），所以不能在集合中放入nil值NSObject *obj1 = [[NSObject alloc] init];NSObject *obj2 = [NSNull null];NSObject *obj3 = [NSObject new];NSObject *obj4;NSArray *arr1 = [NSArray arrayWithObjects:obj1, obj2, obj3, obj4, nil];NSLog(@"arr1 count: %ld", [arr1 count]);    //arr1 count: 3
        NSObject *obj1;NSObject *obj2 = [[NSObject alloc] init];NSObject *obj3 = [NSNull null];NSObject *obj4 = [NSObject new];NSArray *arr2 = [NSArray arrayWithObjects:obj1, obj2, obj3, obj4, nil];NSLog(@"arr2 count: %ld", [arr2 count]);   //arr2 count: 0//有异常！NSObject *obj1 = [NSNull null];NSArray *arr1 = [NSArray arrayWithObjects:@"One", @"TWO", obj1, @"three" ,nil];for (NSString *str in arr1) {NSLog(@"array object: %@", [str lowercaseString]);}//修改NSObject *obj1 = [NSNull null];NSArray *arr1 = [NSArray arrayWithObjects:@"One", @"TWO", obj1, @"three" ,nil];for (NSString *str in arr1) {if (![str isEqual:[NSNull null]]){NSLog(@"array object: %@", [str lowercaseString]);}}}return 0;
}