For Loop to add two columns in Excel

Roshan_K 

I would say for loops are for situations where you know how many times, at most, the loop should iterate whereas Do loops are for instances where you want the loop to repeat while or until a particular condition is reached.

Using your example data (assuming it is in A1:B12 and also assuming your worksheet is the active worksheet as I did not fully qualify my ranges by specifying which worksheet, like Worksheets("Sheet1").Range("A1")):

Sub AddCols1()
     Dim i As Long
     
     For i = 1 To 12
          Range("C" & i).Value = Range("A" & i).Value + Range("B" & i).Value
     Next i
     
End Sub

Sub AddCols2()
     Dim cell As Range
     
     For Each cell In Range("A1:A12").Cells
          cell.Offset(0, 2).Value = cell.Value + cell.Offset(0, 1).Value
     Next cell
     
End Sub

Sub AddCols3()
     Dim i As Long
     
     i = 1
     
     Do While Range("A" & i).Value <> ""
          Range("C" & i).Value = Range("A" & i).Value + Range("B" & i).Value
          i = i + 1
     Loop
     
End Sub