Use VBA to autofill a range of row based on user input

Liosnia 

For example:

Sub CreateTriangle()
    Dim i As Long
    Dim j As Long
    Dim c As Long
    Dim n As Long
    n = Application.InputBox(Prompt:="How many rows do you want to fill?", Type:=1)
    If n < 1 Then
        Beep
        Exit Sub
    End If
    Application.ScreenUpdating = False
    c = 65
    For i = 1 To n
        For j = 1 To i
            Cells(i + 1, j).Value = Chr(c)
            c = c + 1
            If c > 90 Then c = 65
        Next j
    Next i
    Application.ScreenUpdating = True
End Sub