Basic addition sub

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

addValue = Application.InputBox(Prompt:="Input a value to add.", _ 
             Title:="Add Number", Default:=180, Type:=1) 'The underscore character is a continuation character.