Does this type of function or technique have a name?

Question

HI there, I'm slightly new to programming, more of a hobby. I am wondering if a the following logic or technique has a specific name, or term. My current project has 7 check boxes, one for each day of the week. I needed an easy to save which boxes were checked.

The following is the method to saved the checked boxes to a single number. Each checkbox gets a value that is double from the last check box. When I want to find out which boxes are checked, I work backwards, and see how many times I can divide the total value by the checkbox value.

private int SetSelectedDays()
{
     int selectedDays = 0;
     selectedDays += (dayMon.Checked) ? 1 : 0;
     selectedDays += (dayTue.Checked) ? 2 : 0;
     selectedDays += (dayWed.Checked) ? 4 : 0;
     selectedDays += (dayThu.Checked) ? 8 : 0;
     selectedDays += (dayFri.Checked) ? 16 : 0;
     selectedDays += (daySat.Checked) ? 32 : 0;
     selectedDays += (daySun.Checked) ? 64 : 0;
     return selectedDays;
}

private void SelectedDays(int n)
{
     if ((n / 64 >= 1) & !(n / 64 >= 2))
     {
          n -= 64;
          daySun.Checked = true;
     }
     if ((n / 32 >= 1) & !(n / 32 >= 2))
     {
          n -= 32;
          daySat.Checked = true;
     }
     if ((n / 16 >= 1) & !(n / 16 >= 2))
     {
          n -= 16;
          dayFri.Checked = true;
     }
     if ((n / 8 >= 1) & !(n / 8 >= 2))
     {
          n -= 8;
          dayThu.Checked = true;
     }
     if ((n / 4 >= 1) & !(n / 4 >= 2))
     {
          n -= 4;
          dayWed.Checked = true;
     }
     if ((n / 2 >= 1) & !(n / 2 >= 2))
     {
          n -= 2;
          dayTue.Checked = true;
     }
     if ((n / 1 >= 1) & !(n / 1 >= 2))
     {
          n -= 1;
          dayMon.Checked = true;
     }
     if (n > 0)
     {
          //log event
     }
}

The method works well for what I need it for, however, if you do see another way of doing this, or a better way to writing, I would be interested in your suggestions.

Answer 1

This resembles bitmasking. When I can find the blog I read this week using this exact example I'll post it!

Ah got it! Here it is.

You can then do things like:

DaysOfWeek week = DaysOfWeek.Sunday | DaysOfWeek.Monday;

to select Sunday and Monday. Or in your example, when you check the value of each checkbox you can do:

DaysOfWeek week = DaysOfWeek.None; // DaysOfWeek.None = 0

if (Monday.Checked)
{
    week |= DaysOfWeek.Monday;
}

and to check if a particular day is set:

DaysOfWeek week = DaysOfWeek.Monday | DaysOfWeek.Tuesday;

// this will be FALSE (so Wednesday will remain unchecked) because "week" contains Monday/Tuesday, but not Wednesday.
if ((week & DaysOfWeek.Wednesday) == DaysOfWeek.Wednesday)
{
    Wednesday.Checked = true;
}

EDIT:

.NET's built-in DayOfWeek does not allow for bitmasking multiple values, so you'll need to roll your own DaysOfWeek enum.

Answer 2

It is called bitmasking and you can do the same thing more easily using an Enum with the Flags attribute.

Answer 3

You could create an enum with all days and mark it with the attribute [Flags] then give each day the same value as your (bla.checked) ? XX..

then you could use +=, and, or to get the same functionality..

so to check if a value contains lets say monday you would do

if (myEnum & Days.Monday == Days.Monday) { ... }

Answer 4

Someone else mentioned bit masking, but I thought I would show you a way to simplify your code.

daySun.Checked = (n & 64) == 64;
daySat.Checked = (n & 32) == 32;
dayFri.Checked = (n & 16) == 16;
dayThu.Checked = (n & 8) == 8;
dayWed.Checked = (n & 4) == 4;
dayTue.Checked = (n & 2) == 2;
dayMon.Checked = (n & 1) == 1;

Answer 5

It's called a bitfield, and yes, it's the most space-efficient way to solve this. Using separate booleans will probably use more memory, but IMO the better readability is worth six bytes or so.

Answer 6

you can use an enum... its more readable and pretty

    public enum daysOfWeek
    {
        Mon = 1, Tue = 2, Wed = 4, Thu = 8, Fri = 16, Sat = 32, Sun = 64
    }

Answer 7

you can hide the complexity in a function: and it's better to bit-shift instead of dividing

private bool get_bit(int val, int idx)
{
  return ((val >> idx) & 1) != 0;
}