10 DIM S1$     'implicitly defined empty string
20 S2$ = ""    'explicitly defined empty string
30 S3$ = "Foo bar baz"
40 S$=S1$ : GOSUB 200
50 S$=S2$ : GOSUB 200
60 S$=S3$ : GOSUB 200
70 END
200 IF LEN(S$)=0 THEN PRINT "Empty string" ELSE PRINT "Non-empty string"
210 RETURN