run code when a cell is changed

I have a drop down menu for the user to select the week number they want to view. Once they select the week I want code to run that will hide all but the data from that week. I wrote the code and it works when I run it as a macro, but I don't know how to make it automatically run once the week number cell is changed. I don't want to have to tell people to select their choice from the drop down menu, and then run the macro manually. I'm sure there has to be a way to insert this code into the worksheet itself, but I am unsure as to how to write it, and where to put it. Many thanks for the help.

Here's my macro code if you're interested:

Sub hideall()
'
' hideall Macro
'


    
    Columns("G:HA").Select
   
   Selection.EntireColumn.Hidden = True
   
      If Range("B1").Value = "Week 26" Then
   Columns("T:AI").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 27" Then
    Columns("AJ:AY").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 28" Then
    Columns("AZ:BO").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 29" Then
    Columns("BP:CE").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 30" Then
    Columns("CF:CU").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 31" Then
    Columns("CV:DK").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 32" Then
    Columns("DL:EA").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 33" Then
    Columns("EB:EQ").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 34" Then
    Columns("ER:FE").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 35" Then
    Columns("FH:FW").Select
   Selection.EntireColumn.Hidden = False
   
   ElseIf Range("B1").Value = "Week 36" Then
    Columns("FX:GM").Select
   Selection.EntireColumn.Hidden = False
   
      ElseIf Range("B1").Value = "Week 37" Then
    Columns("GN:HC").Select
   Selection.EntireColumn.Hidden = False
   
   
   End If
   
End Sub

btw, if it matters, the cell with the drop down menu for week number is cell B1

Put the following into the relevant worksheet module and change the WS_RANGE referemce to suit

Private Sub Worksheet_Change(ByVal Target As Range)
Const WS_RANGE As String = "J:J"      '<<<< change to suit'

    On Error GoTo ws_exit


    If Not Intersect(Target, Me.Range(WS_RANGE)) Is Nothing Then
         Call hideall
    End If

ws_exit:

End Sub

Dave H

I tried the code, but maybe I don't understand what you mean by change to suit. I am unfamiliar with what WS_RANGE is, so it's hard for me to figure it out. I tried putting in B1 as the range, but it pulled up a box that looked like it wanted me to save something and I could neither save, nor close out, and ended up having to force close excel.

gryffin13,

WS_RANGE is specifying the column the change event will trigger on. If your week number is in column A then change "J:J" to "A:A" or if in column L change to "L:L" etc.

Hope that helps

Dave H