if then till last row - excel

Question

I want that if cell in column e is not blank but cell in column i is blank then write unregister in column i or else write what ever written in column i.
Please help - I have used below code:
Sub Simple_If()
Dim lastrow As Long
lastrow = Cells(Rows.Count, "F").End(xlUp).Row
If Range("e2:e" & lastrow).Value <> "" And Range("i2:i" & lastrow).Value = "" Then
Range("i2:i" & lastrow).Value = "unregister"
End If
End Sub

Answer 1

The reason your code was not working is because you can't get .value of a .range (Range("e2:e" & lastrow).Value <> ""). Instead, use a for loop to iterate through each cells value individually.
I have commented each line of the code below to help you understand what is happening.
To make this work, change SO.xlsm to the name of your workbook and 63649177 to the name of your worksheet.
Sub Simple_If()
Dim WB As Workbook ' workbook - full name of the file containing data.
Dim WS As Worksheet ' worksheet - worksheet within workbook containing data.
Dim lRow As Long ' last row - find last row containing data
Dim i As Long ' iteration - used for loop
Set WB = Workbooks("SO.xlsm") ' set the name of the workbook here
Set WS = WB.Worksheets("63649177") ' set the name of the worksheet here
lRow = WS.Cells(WS.Rows.count, "E").End(xlUp).Row ' find the last row of E in the WS object, not user defined.
Set Rng = WS.Range("E2:E" & lRow) ' set the initial range
For i = 2 To lRow ' from line 2 to the last row, repeat this loop
If WS.Range("E" & i).Value <> "" And WS.Range("I" & i).Value = "" Then ' if E contains data and I does not then
WS.Range("I" & i).Value = "unregister" ' fill cell with "unregister"
End If ' end if
Next ' cycle through next iteration of loop
End Sub
Output

Answer 2

Loop Through Rows
You were trying to check the values of two ranges "E2:E & LastRow" and "I2:I & LastRow" in one go, but you cannot do that. You have to loop through the rows of the ranges and check each cell i.e. "E2", "E3", "E4" ... "E" & LastRow and "I2", "I3", "I4" ... "I" & LastRow. For this task a For Next loop can used.
The 1st code is showing how it is done using Range.
The 2nd code is showing how it is done using column strings (letters) with Cells.
The 3rd code is showing how it is done using column numbers with Cells.
The 4th code is showing how you can define the column ranges (rng1, rng2) and use Cells with one parameter.
The 5th code is showing how you can define constants to store the so called 'magic' characters and later quickly access (change) them. It is also modified to be able to change the resulting column (tgtCol).
Range might seem easier, but you have to learn Cells, too, e.g. because you cannot loop through columns using Range, you have to use column numbers with Cells.
Study the first three codes closely, and you will learn the differences soon enough.
The Code
Option Explicit
Sub fillSimpleRangeVersion()
' Calculate the last non-blank cell in column "F".
Dim LastRow As Long
LastRow = Range("F" & Rows.Count).End(xlUp).Row
Dim i As Long
' Loop through the rows from 2 to LastRow.
For i = 2 To LastRow ' i will change: "2, 3, 4 ... LastRow"
' Check that current cell in column "E" is not blank and
' that current cell in column "I" is blank:
' If not E2 blank and I2 blank then,
' If not E3 blank and I3 blank then ...
' If not E & LastRow blank and I & LastRow blank then.
If Not IsEmpty(Range("E" & i)) And IsEmpty(Range("I" & i)) Then
' If true, write "unregister" to current cell in column "I".
Range("I" & i).Value = "unregister"
' The Else statement is not needed, because you only write when
' the condition is true.
Else
' If not true, do nothing.
End If
Next i
End Sub
Sub fillSimpleCellsStringsVersion() ' Column Strings E, F, I
Dim LastRow As Long
LastRow = Cells(Rows.Count, "F").End(xlUp).Row
Dim i As Long
For i = 2 To LastRow
If Not IsEmpty(Cells(i, "E")) And IsEmpty(Cells(i, "I")) Then
Cells(i, "I").Value = "unregister"
End If
Next i
End Sub
Sub fillSimpleCellsNumbersVersion() ' Column Numbers 5, 6, 9
Dim LastRow As Long
LastRow = Cells(Rows.Count, 6).End(xlUp).Row
Dim i As Long
For i = 2 To LastRow
If Not IsEmpty(Cells(i, 5)) And IsEmpty(Cells(i, 9)) Then
Cells(i, 9).Value = "unregister"
End If
Next i
End Sub
Sub fillSimpleCellsVersionWithRanges()
Dim LastRow As Long
LastRow = Cells(Rows.Count, "F").End(xlUp).Row
Dim rng1 As Range
Set rng1 = Range("E2:E" & LastRow)
Dim rng2 As Range
Set rng2 = Range("I2:I" & LastRow)
Dim i As Long
For i = 1 To rng1.Rows.Count
If rng1.Cells(i).Value <> "" And rng2.Cells(i).Value = "" Then
rng2.Cells(i).Value = "unregister"
End If
Next i
End Sub
Sub fillSimpleCellsExpanded()
Const FirstRow As Long = 2 ' First Row
Const LastRowCol As Variant = "F" ' The column to Calculate Last Row
Const Col1 As Variant = "E" ' Column 1
Const Col2 As Variant = "I" ' Column 2
Const tgtCol As Variant = "I" ' Target Column, the Column to Write to
' You want to write to the same column "CritCol2 = tgtCol", but if you
' want to write to another column, you can easily change "tgtCol".
Const Criteria As String = "unregister" ' Write Criteria
Dim LastRow As Long
LastRow = Cells(Rows.Count, LastRowCol).End(xlUp).Row
Dim i As Long
For i = FirstRow To LastRow
If Not IsEmpty(Cells(i, Col1)) And IsEmpty(Cells(i, Col2)) Then
Cells(i, tgtCol).Value = Criteria
Else
' The following line is only needed if "CritCol2" is different
' than "tgtCol".
Cells(i, tgtCol).Value = Cells(i, Col2).Value
End If
Next i
End Sub