NSString大小写转换

NSString *string = @"How are you";
NSLog(@"uppercaseString:%@", string.uppercaseString);       //全部大写
NSLog(@"lowercaseString:%@", string.lowercaseString);       //全部小写
NSLog(@"capitalizedString:%@", string.capitalizedString);   //首字母大写

打印数据：

uppercaseString:HOW ARE YOU
lowercaseString:how are you
capitalizedString:How Are You