NSNumber是NSValue的子类，它提供C基本类型的值。char，short等等
1. 创建NSNumber对象的类方法（工厂方法）
+ (NSNumber *)numberWithBool:(BOOL)value
这个value的值时BOOL类型的
+ (NSNumber *)numberWithChar:(char)value
这个char是带符号的
+ (NSNumber *)numberWithDouble:(double)value
+ (NSNumber *)numberWithFloat:(float)value
+ (NSNumber *)numberWithInt:(int)value
+ (NSNumber *)numberWithInteger:(NSInteger)value
+ (NSNumber *)numberWithLong:(long)value
+ (NSNumber *)numberWithLongLong:(long long)value
+ (NSNumber *)numberWithShort:(short)value
+ (NSNumber *)numberWithUnsignedChar:(unsigned char)value
这个char是不带符号的
+ (NSNumber *)numberWithUnsignedInt:(unsigned int)value
+ (NSNumber *)numberWithUnsignedInteger:(NSUInteger)value
注意，NSInteger和NSUInteger的区别，多了一个U，也就是unsigned的意思，一个带符号，一个不带符号
+ (NSNumber *)numberWithUnsignedLong:(unsigned long)value
+ (NSNumber *)numberWithUnsignedLongLong:(unsigned long long)value
+ (NSNumber *)numberWithUnsignedShort:(unsigned short)value
2. 初始化一个NSNumber对象
- (NSNumber *)initWithBool:(BOOL)value
- (NSNumber *)initWithChar:(char)value
- (NSNumber *)initWithDouble:(double)value
- (NSNumber *)initWithFloat:(float)value
- (NSNumber *)initWithInt:(int)value
- (NSNumber *)initWithInteger:(NSInteger)value
- (NSNumber *)initWithLong:(long)value
- (NSNumber *)initWithLongLong:(long long)value
- (NSNumber *)initWithShort:(short)value
- (NSNumber *)initWithUnsignedChar:(unsigned char)value
- (NSNumber *)initWithUnsignedInt:(unsigned int)value
- (NSNumber *)initWithUnsignedInteger:(NSUInteger)value
- (NSNumber *)initWithUnsignedLong:(unsigned long)value
- (NSNumber *)initWithUnsignedLongLong:(unsigned long long)value
- (NSNumber *)initWithUnsignedShort:(unsigned short)value