Someone that I work with (in another office) asked me if I could help him with an issue he had. In a nutshell, he basically had a spreadsheet with dates when a job needed to be accomplished. He updates this every day for all the jobs that are being completed. He wanted an easy way to figure out what the next due date would be, which was 180 days later. So basically the Date + 180.

I elected to write this for him as a Subroutine that would kick off whenever he pressed CTRL+SHIFT+A

The code works great, but seeing as how I'm still fairly new to all this I was wondering if you would have done this differently? I'd love to be able to use this as an opportunity to improve. Thanks!
The code has comments all over the place, but if you need clarification, let me know.


In essense, the user selects a cell and executes the program. Message box asks for a number, if no number is provided it gives an error statement and tries again. At any time the user can cancel. If there's a number, or a date in this cell, the values are added together, and then the cell is replaced with this new value. If not, an error message is displayed. Once again, the user can cancel whenever they want.

Thanks!!!!
Code:
Sub addValue()
'
' Take a number and add a new number to it.
'
'To complete this transaction well need to create three variables.
'The variable "addValue" will be collected as the number to be added to the existing value.
'The term "Dim" allows us to create a new variable to be used temporarily throughout the function.
 

'Now we ask for a value to add, and supply the default value of "180".  We check to see if the value is a number, and if not we supply an error message.
Dim addValue
Dim testValue
Do
addValue = InputBox(Prompt:="Input a value to add.", _
              Title:="Add Number", Default:=180) 'The underscore character is a continuation character.

If addValue = "" Then
    Exit Sub
End If

testValue = IsNumeric(addValue)
If testValue = False Then
   testValue = MsgBox("This is not a number Value.", vbRetryCancel)
End If

If testValue = vbCancel Then
    Exit Sub
End If

'The below "loop until testValue = True" causes the above statement to repeat until the user supplies a number value.
Loop Until testValue = True


'Whatever the user supplies is returned by the function and then added to the "addValue" variable.
'Now we need to determine what we are working with, a Date or a Number.
'To do this we use two functions, "IsDate()" and "IsNumeric()".  These will return a boolean value (True/False)
'We also specify a small bit of code to be processed if the function returned "True".
'First we check if the value is a date, and if so, we process the code with this format.
If IsDate(ActiveCell) Then
Dim firstDate As Date
Dim newDate As Date

    firstDate = ActiveCell.Value   'This takes the current cell value and places that value into the firstDate variable.
    newDate = firstDate + addValue 'Here we add the two variables together and place that value into the newDate variable.
    Selection.Value = newDate      'Lastly, we take this new value, and put it into the active cell, replacing the old value.
    
'If the first test was false, we have another test performed to see if the value is at least a number that can still be added.
ElseIf IsNumeric(ActiveCell) Then
Dim firstNum As Integer
Dim newNum As Integer
    firstNum = ActiveCell.Value   'This takes the current cell value and places that value into the firstNum variable.
    newNum = firstNum + addValue  'Here we add the two variables together and place that value into the newNum variable.
    Selection.Value = newNum      'Lastly, we take this new value, and put it into the active cell, replacing the old value.
'If the two tests were false, we display an error message, and then exit the subroutine.
Else: MsgBox "You cannot add this number."
        Exit Sub
End If

'Success!
End Sub