need help with error : compile error expected array

I am trying to do a lookup function but it does not compile error occurs at this line:

ReDim myarr(last_row)

Could someone please help?

Function look(a As String) As Integer  'a is string looking up in cell

Dim myarr As String
Dim index As Long, row_index As Long, i As Integer
row_index = 2
Dim last_row As Integer

last_row = lookup.Range("d2").End(xlUp).Row

MsgBox last_row

ReDim myarr(last_row) 'redefine dimensions of array since have  last row

    For i = 1 To last_row
    
            myarr(index) = lookup.Cells(row_index, 4).Value 'col D string values stored in array
                
                    If a = myarr(index) Then
                        look = lookup.Cells(row_index, 3).Value
                        
                        MsgBox look
                        
                    Else
                    End If
            row_index = row_index + 1
            index = index + 1
    Next

End Function

When you declared the myarr variable, you declared it as a string rather than an array that contains strings.
Change

 dim myarr as string

to

 dim myarr() as string

many thanks works perfect now

You're welcome!