Should I use byte or int?

Question

I recall having read somewhere that it is better (in terms of performance) to use Int32, even if you only require Byte. It applies (supposedly) only to cases where you do not care about the storage. Is this valid?

For example, I need a variable that will hold a day of week. Do I

int dayOfWeek; 

or

byte dayOfWeek; 

EDIT: Guys, I am aware of DayOfWeek enum. The question is about something else.

Answer 1

Usually yes, a 32 bit integer will perform slightly better because it is already properly aligned for native CPU instructions. You should only use a smaller sized numeric type when you actually need to store something of that size.

Answer 2

You should use the DayOfWeek enum, unless there's a strong reason not to.

DayOfWeek day = DayOfWeek.Friday; 

To explain, since I was downvoted:

The correctness of your code is almost always more critical than the performance, especially in cases where we're talking this small of a difference. If using an enum or a class representing the semantics of the data (whether it's the DayOfWeek enum, or another enum, or a Gallons or Feet class) makes your code clearer or more maintainable, it will help you get to the point where you can safely optimize.

int z; int x = 3; int y = 4; z = x + y; 

That may compile. But there's no way to know if it's doing anything sane or not.

Gallons z; Gallons x = new Gallons(3); Feet y = new Feet(4); z = x + y; 

This won't compile, and even looking at it it's obvious why not - adding Gallons to Feet makes no sense.