VBA Excel - Hàm Đổi ký tự trong chuỗi

Public Function f_doikytu(chuoikytu1 As String, kytucu1 As String, kytumoi1 As String)
 solanxuathien = 0
If UCase(kytucu1) = UCase(kytumoi1) Then

  GoTo thoat

  End If
 dodaikytucu1 = Len(kytucu1)

  dodaikytumoi1 = Len(kytumoi1)

  dodaichuoi1 = Len(chuoikytu1)
If dodaichuoi1 = 0 Or dodaikytucu1 = 0 Then

  GoTo thoat

  End If

  

  For i = 1 To dodaichuoi1

  For m = i To dodaichuoi1

  kytucat1 = Mid(chuoikytu1, m, dodaikytucu1)

  If UCase(kytucat1) = UCase(kytucu1) Then

  solanxuathien = solanxuathien + 1

  End If

  Next m

  Next i

  

  For i = 1 To solanxuathien

  dongtext = f_laplai_chuoi(chuoikytu1, kytucu1, kytumoi1)

  chuoikytu1 = dongtext

  Next
 
If solanxuathien = 0 Then

  dongtext = chuoikytu1

  End If
 f_doikytu = dongtext
thoat:
End Function
Public Function f_laplai_chuoi(chuoikytu As String, kytucu As String, kytumoi As String)
If UCase(kytucu) = UCase(kytumoi) Then

  GoTo thoat

  End If
 Dim chuoikytumoi As String
 dodaikytucu = Len(kytucu)

  dodaikytumoi = Len(kytumoi)

  dodaichuoi = Len(chuoikytu)
 chuoikytumoi = ""

  

  If dodaichuoi = 0 Or dodaikytucu = 0 Then

  GoTo thoat

  Else
stt = 0

  

  For i = 1 To dodaichuoi

  kytucat = Mid(chuoikytu, i, dodaikytucu)

  If UCase(kytucat) = UCase(kytucu) Then

  stt = stt + 1

  

  If i = 1 Then

  

  chuoikytumoi = kytumoi & Right(chuoikytu, dodaichuoi - dodaikytucu)

  GoTo thoat

  End If

  

  If i = dodaichuoi Then

  chuoikytumoi = Left(chuoikytu, dodaichuoi - dodaikytucu) & kytumoi

  GoTo thoat

  End If

  

  

  chuoikytumoi = Left(chuoikytu, i - 1) & kytumoi & Right(chuoikytu, dodaichuoi - dodaikytucu - (i - 1))


End If

  Next

  End If
If stt = 0 Then

  chuoikytumoi = chuoikytu

  End If


thoat:
f_laplai_chuoi = chuoikytumoi


End Function