vba coding "do until or while" and "loop"

The problem is that score is a number and will always be <> "".

Sub Example2()
    Dim score As Integer
    Dim x As Integer
    x = 2

    With Sheets("sheet1")
        Do While .Cells(x, 2).Value <> ""

            score = .Cells(x, 2).Value

            If score >= 90 And score <= 100 Then
                .Cells(x, 3).Value = "A"

            ElseIf score > 79 And score < 90 Then
                .Cells(x, 3).Value = "B"

            ElseIf score > 69 And score < 80 Then
                .Cells(x, 3).Value = "C"

            ElseIf score > 59 And score < 70 Then
                .Cells(x, 3).Value = "D"

            ElseIf score < 60 Then
                .Cells(x, 3).Value = "F"

            Else
                .Cells(x, 3).Value = ""

            End If
            x = x + 1

        Loop

    End With
End Sub

Petrie Manuel, I am not sure in what case you want to use your Else statement:

Sheets("Sheet1").Cells(x, 3).Value = "" 

Since if the score is less than 60 you will put an F, no ?

Anyway, to simplify your code and logic statements I used Select Case.

Sub Grades()

    Dim score       As Integer
    Dim x           As Integer
    Dim sht1        As Worksheet

    Set sht1 = ThisWorkbook.Worksheets("sheet1")

    ' if your first row is for table headers
    x = 2

    With sht1
        Do While .Cells(x, 2).Value <> ""
            score = .Cells(x, 2).Value

            Select Case score
                Case Is >= 90
                    .Cells(x, 3).Value = "A"

                Case Is >= 80
                    .Cells(x, 3).Value = "B"

                Case Is >= 70
                    .Cells(x, 3).Value = "C"

                Case Is >= 60
                    .Cells(x, 3).Value = "D"

                Case Is < 60
                     .Cells(x, 3).Value = "F"

                Case Else
                    .Cells(x, 3).Value = ""

            End Select

            x = x + 1
        Loop

    End With

End Sub

since:

• numbers in column "B" are percentages -> always between 0 and 100

• your need is parsing them by multiples of 10

then you could go like follows:

Option Explicit

Sub Grades()
    Dim cell As range
    With Sheets("scores") '<--| change "scores" with your actual sheet name
        For Each cell In .range("B1", .Cells(.Rows.Count, "B").End(xlUp)).SpecialCells(xlCellTypeConstants, xlNumbers) '<--| loop through "numeric" column "B" cells down to last non empty one only
            cell.Offset(, 1) = Choose(Int(cell.value / 10) + 1, "F", "F", "F", "F", "F", "F", "D", "C", "B", "A", "A") 
        Next cell
    End With
End Sub

should your percentages come from formulas then simply substitute xlCellTypeConstants with xlCellTypeFormulas