OPTION CHARACTER BYTE
LET infile$="ABC.txt"
LET outfile$="QWE.txt"
OPEN #1:NAME infile$
OPEN #2:NAME outfile$ 
ERASE #2
ASK #1: FILESIZE n
LET s$=""
FOR i=1 TO n
   CHARACTER INPUT #1: s$(i:i)
NEXT i
FOR i=1 TO n
   LET b$=UCASE$(s$)
NEXT i
PRINT #2:b$;
CLOSE #1
CLOSE #2
END