Explanation of the VBA code for the calendar

The article about the way to build an automatic calendar is one of the most viewed in this website. But it is also the one with the most comments about the vba code.

The purpose of this article is to explain each lines of code and the logic of the program.

Sub Hide_Day()
Dim Num_Col As Long
   'This instruction cleans the content of the cells in your calendar
   Range("B7:AF13").ClearContents
   For Num_Col = 30 To 32
   ' Test if the month of the cells (row 6) is the same of the month selected (cell A1 or cells(1,1))
     If Month(Cells(6, Num_Col)) >= Cells(1, 1) Then
        Columns(Num_Col).Hidden = True
     Else
        Columns(Num_Col).Hidden = False
     End If
   Next
End Sub

Line 1: Creation of the name of the subroutine

In any VBA program all the code is written inside subroutines (Sub). Each subroutine must have a unique name in the projet.

This name will be used in the calendar project to link the code with the dropdown list.

Sub Hide_Day()

Line 2 : Declare the variable

To evaluate the day's value in the different columns, we need a create variable in order to read each column index (1, 2, 3, ....)

The variable Num_Col is declared (Dim) as a Whole Number (As Long) because the column index is obviously without decimal

Dim Num_Col As Long

Line 3 : Beginning of the loop

Now, we are going to create a loop to extend the variable Num_Col from 30 till 32.

For Num_Col = 30 To 32 

The reason why we start at the value 30 it's because for any month, the days 29, 30 et 31 will be always in the column 30, 31 and 32

What is the value of the dates in column 30, 31 and 32

Line4 : Test between the month calculated in the cells and the month selected

Here is the trick of the program 😉😎

How Excel calculates date?

As you know, all the months have 28 days. But February could have 29 days each 4 years and 4 months have 30 days (April, June, September, November).

Just like that it seems complex to create a test for each case. But on the other hand, Excel calculates precisely a date even if the number of days to add extend the end of the month.

For instance, if we add 30 days to the 1st February 2019, Excel will return the date of the 3rd March 2019.

=DATE(2019;2;1)+30 => 03/03/2019

Calculated dates when February is selected

How to code a cell in VBA

In VBA, to read the contain of a cell, you just have to write Cells(index row, index column). So for A1, you will write Cells(1, 1) and for the cell AD6 with the day 29, the code is Cells(6, 30)

But you can also replace one of the arguments of Cells by a variable like this Cells(6, Num_Col)

Construction of the test

Back to the calendar, for the month February 2019, the columns 30, 31 and 32 will have dates of March (and not February) because of the rule explain in the previous formula.

So, we will write a test between the month (return by the VBA function Month) of the column 30, 31 et 32 and the value returned by the dropdown menu for the month.

Result returns by the dropdown menu

So, the test will check if the month in the cells AD6, AE6 and AF6 (or Cells(6, 30), Cells(6, 31) et Cells(6,32)) is greater or equal to A1 (the cell linked to the dropdown menu for the month). But we don't need to test the 3 columns, the variable will do it for us 😀

      If Month(Cells(6, Num_Col)) >= Cells(1, 1) Then

Line 5 : Hide the column

If the test is True, the column Num_Col is hidden (Hidden = True).

     Columns(Num_Col).Hidden = True

Line 6 and 7 : Un-hide the column

Otherwise (Else), which it means the test is False, then the column Num_Col is un-hidden (Hidden = False)

      Else
         Columns(Num_Col).Hidden = False

This test looks stupid but in the case your selected month has 31 days, you want to be able to display the previous column hidden (sooo clever 😉)

Line 8 and 9 : Close the instructions

In VBA, when you create a test or a loop, you must indicate when the test or the loop is ended.

The end of the test If is End If, and the the loop For, you must write the instruction Next

     End If
   Next  

Line 10 : Clear the data

After the loop on the 3 columns, the program will clear the contain of the range B6 to AF13 Range("B6:AF13") with the instruction ClearContents

   Range("B6:AF13").ClearContents  

Line 11 : End of the subroutine

Exactly like to indicate the end of a test or a loop, you must indicate that your subroutine is ended with the instruction End Sub

End Sub

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