  100 REM PURPOSE: VERIFY 'VIRTUAL' VARIABLES
  110 REM  AUTHOR: HOWARD WULF, AF5NE
  120 REM    DATE: 2017-04-09
  130 REM    NOTE: OPTION VERSION "BYWATER"
  140 REM
  150 REM
  200 OPTION BASE 1
  210 LET F = 3
  220 OPEN "VIRT_7.DAT" FOR VIRTUAL AS # F
  230 LET N = LOF( F )
  240 IF N <= 0 THEN 999
  250 DIM # F, A( N ) AS BYTE
  260 REM
  270 GOSUB 800
  280 REM
  290 FOR I = 1 TO N
  300   LET A(I) = A(I) + 32
  310 NEXT I
  320 REM
  330 GOSUB 800
  340 REM
  350 FOR I = 1 TO N
  360   LET A(I) = A(I) - 32
  370 NEXT I
  380 REM
  390 GOSUB 800
  400 REM
  410 GOTO 999
  800 REM READ THE FILE
  810 FOR I = 1 TO N
  820   PRINT A(I);
  830 NEXT I
  840 PRINT
  850 RETURN
  860 REM
  999 END
