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Code
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Sub Mark_with_an_X()
continue = True
Do While continue = True
Do
Repeat = False
myColumn = InputBox("Enter a column letter from A to Z:", "Choose a column", "A")
'******CODE BELOW TO VALIDATE USER INPUT*************
If myColumn = "" Then End
If Len(Trim(myColumn)) <> 1 Then
MsgBox "You must enter exactly ONE letter."
Repeat = True
End If
If CBool((Asc(myColumn) < 91 And Asc(myColumn) > 64) Or (Asc(myColumn) < 123 And Asc(myColumn) > 96)) = False Then
MsgBox "You must enter a letter of the alphabet. No symbols or numbers."
Repeat = True
End If
Loop While Repeat = True
'*********DONE VALIDATING THE COLUMN LETTER INPUT************
Do
Repeat = False
myRow = InputBox("Enter a row number from 1 to 99:", "Choose a row", "1")
'******CODE BELOW TO VALIDATE ROW INPUT********************
If myRow = "" Then End
If Len(Trim(myRow)) > 2 Or Len(Trim(myRow)) < 1 Or Trim(myRow) = "0" Then
MsgBox "Your input is invalid. MUST BE a number from 1 to 99"
Repeat = True
End If
If CByte(myRow) < 1 Or CByte(myRow) > 99 Then
MsgBox "Your input is invalid. MUST BE a number from 1 to 99"
Repeat = True
End If
Loop While Repeat = True
'******DONE VALIDATING ROW NUMBER INPUT*************************
'****PLACE THE X-MARK NOW*****************************
myCellAddress = myColumn & myRow
Range(myCellAddress).Value = "X"
'*********ASK USER WHETHER TO CONTINUE OR QUIT****************
userDecision = MsgBox("Would you like to mark another cell?", vbOKCancel)
If userDecision <> 1 Then continue = False
Loop
End Sub