Sergey is right. An array would be simpler, but in any case, for the moment, maybe this would work for you. It can be simplified further with an array.

LOCAL llOk
llOk = .T.

LC = ALLTRIM(DIRETO.REG)

IF LEN(ALLTRIM(lc)) = 9
  FOR lnCounter = 1 TO LEN(ALLTRIM(lc)) - 1
    lcVarName = 'R' + ALLTRIM(STR(lnCounter))
    &lcVarName = VAL(SUBSTR(lc,lnCounter,1))
  ENDFOR

  DV = VAL(SUBSTR(9,1))

  Sum = (R1 * 8) + (R2 * 6) + (R3 * 4) + (R4 * 2) + (R5 * 3) + (R6 * 5) + (R7 * 9) + (R8 * 7)

  REST1 = MOD(Sum, 11)

  DO CASE
  CASE REST1 = 0
  DV1 = 5
  CASE REST1 = 1
  DV1 = 0
  OTHER
  DV1 = 11 - REST1
  ENDCASE

  IF DV1 # DV
    llOkk = .F.
  ENDIF
ELSE
  llOk = .F.
ENDIF

IF !llOk
  MESSAGEBOX ("invalid code") 
ENDIF

>Please take a look at the code below:
>
>** the last one is the verify digit
>
>
>LN = VAL (DIRETO.REG)
> endif
>
>
>FOR lnCounter = 1 TO LEN(ALLTRIM(STR(ln)))
>lcVarName = 'lcVarName' + ALLTRIM(STR(lnCounter))
>&lcVarName = INT(VAL(substr(trans(ln),lnCounter,1)))
>ENDFOR
>
>R1 = lcVarName1
>R2 = lcVarName2
>R3 = lcVarName3
>R4 = lcVarName4
>R5 = lcVarName5
>R6 = lcVarName6
>R7 = lcVarName7
>R8 = lcVarName8
>DV = lcVarName9
>
>
>Sum = (R1 * 8) + (R2 * 6) + (R3 * 4) + (R4 * 2) + (R5 * 3) + (R6 * 5) + (R7 * 9) + (R8 * 7)
>
>REST1 = MOD(Sum, 11)
>
>DO CASE
>CASE REST1 = 0
>DV1 = 5
>CASE REST1 = 1
>DV1 = 0
>OTHER
>DV1 = 11 - REST1
>ENDCASE
>
>IF DV1 # DV
>
>= MESSAGEBOX ("invalid code")