Increase number of column and write into selected cell - vba

Question

Good day,
I need help with a little problem. I have a macro which compares cell with range of cells. If the equal cell is not found, it will add the cell at the end of the range. My problem is with equal cell. If it finds it, I need to add 3 to column index and write "X" into this cell.
I have solution for unequal cell but i dont know how to increase column index and write into the cell.
I have this so far:
Sub Compare()
Dim i As Integer
'Comparing cell is from another workbook
Selection.Copy
Windows("zzz.xlsm").Activate
Range("A2").Select
ActiveSheet.Paste
i = 2
Do While Cells(i, 3).Value <> ""
Set FirstRange = Range("C" & i)
If FirstRange.Value = Cells(2, 1).Value Then
MsgBox "Found"
Exit Do
End If
i = i + 1
Loop
If MsgBox = True Then
'Missing code
Else
Range("A2").Select
Selection.Copy
ActiveSheet.Range("E" & Rows.Count).End(xlUp).Offset(1).Select
ActiveSheet.Paste
End If
End Sub
I will appreciate any advice. Thank you for your time.

Answer 1

Sub Compare()
Dim i As Integer
'Comparing cell is from another workbook
Selection.Copy
Windows("zzz.xlsm").Activate
Range("A2").Select
ActiveSheet.Paste
i = 2
Do While Cells(i, 3).Value <> ""
Set FirstRange = Range("C" & i)
If FirstRange.Value = Cells(2, 1).Value Then
MsgBox "Found"
Exit Do
End If
i = i + 1
Loop
If MsgBox = True Then
Cells(i, 6) = "X" 'used to be Missing code
Else
Range("A2").Select
Selection.Copy
ActiveSheet.Range("E" & Rows.Count).End(xlUp).Offset(1).Select
ActiveSheet.Paste
End If
End Sub