[RESOLVED] Logic With days

Hi All,

We have a system were a user chooses a combination of days from a calander. We then insert a values in the databse based on the following

Sunday - 1
Monday - 2
Tuesday - 4
Wednesday - 8
Thursday - 16
Friday - 32
Saturday - 64

So if they picked Monday and Friday we would insert 34, or if they picked Monday,Tuesday and Thursday we would insert 22.

Now my question is how do I reverse this easily in code, to find out what days they have picked. So I get fed 22 from the database how do I figure out what combination of days make up that value.

Sorry it sounds a bit like a homework project bit it really isn't.
The only thing I can think of is creating the mother of all case statements but I know there must be a better way.

You don't have to but I would suggest defining an enumeration to represent the days.

http://www.vbforums.com/showthread.php?t=502644

The logic is still pretty much the same even if you don't use an enumeration, i.e. bitwise operations, e.g.

vb.net Code:

Dim days As Integer = 2 Or 32 'Monday and Friday
 
If (days And 1) = 1 Then
    MessageBox.Show("Sunday")
Else
    MessageBox.Show("Not Sunday")
End If
 
If (days And 2) = 2 Then
    MessageBox.Show("Monday")
Else
    MessageBox.Show("Not Monday")
End If
 
If (days And 4) = 4 Then
    MessageBox.Show("Tuesday")
Else
    MessageBox.Show("Not Tuesday")
End If
 
If (days And 8) = 8 Then
    MessageBox.Show("Wednesday")
Else
    MessageBox.Show("Not Wednesday")
End If
 
If (days And 16) = 16 Then
    MessageBox.Show("Thursday")
Else
    MessageBox.Show("Not Thursday")
End If
 
If (days And 32) = 32 Then
    MessageBox.Show("Friday")
Else
    MessageBox.Show("Not Friday")
End If
 
If (days And 64) = 64 Then
    MessageBox.Show("Saturday")
Else
    MessageBox.Show("Not Saturday")
End If

Code:

---

    Dim tmp as Integer = 64 ' Change this to the value from the Database
    Dim strDays as String = String.Empty
    If tmp >= 64 Then
        strDays = "Sat"
        tmp = tmp Mod 64
    End If
    If tmp >= 32 Then
        strDays = "Fri" + strDays
        tmp = tmp Mod 32
    End If
    If tmp >= 16 Then
        strDays = "Thu" + strDays
        tmp = tmp Mod 16
    End If
    If tmp >= 8 Then
        strDays = "Wed" + strDays
        tmp = tmp Mod 8
    End If
    If tmp >= 4 Then
        strDays = "Tue" + strDays
        tmp = tmp Mod 4
    End If
    If tmp >= 2 Then
        strDays = "Mon" + strDays
        tmp = tmp Mod 2
    End If
    If tmp >= 1 Then
        strDays = "Sun" + strDays
        tmp = tmp Mod 1
    End If
    MessageBox.Show(strDays)

---

There is better code out there, but this will sure help you figure out to solve your problem.

Thanks both.
Have never used "and" and "or" Bitwise Operators for anything other than booleans and that was a long time ago.
Anyway I lied a little by posting this in the vb.net forum, as ideally I want to do this all at the tsql level (though worst come to worst I would have done it in code), quick google search gave me.

http://sqlfool.com/2009/02/bitwise-operations/

Which shows me how to do the same thing in sql.
So thanks for your help.

Quote:

---

Originally Posted by Oliver1

Have never used "and" and "or" Bitwise Operators for anything other than booleans and that was a long time ago

---

If you used them with Booleans then they were logical operators, not bitwise operators. Bitwise operations are basically logical operations at the bit level, where 1 is true and 0 is false. When you perform a bitwise operation on two values you basically perform a logical operation on each pair of corresponding bits.