1 NSArray a = @[ @"aaa" ,@"bbb" ,@"ccccc" ]
id obj2 = a[0]
id obj2 = dict[@"key1"]
NSNumber *number; number = @'X'; number = @12345; number = @12345ul; number = @12345ll; number = @123.45f; number = @123.45; number = @YES;
property属性简化
property方便自动生成变量的getter 和setter。在.h文件中声明之后，不需要在.m文件中加上@synthesize关键字
3 typedef enum Week:NSUInteger{ Moday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
}Week;