100 rem ROT-13
110 cls : rem  110 HOME for Applesoft BASIC
120 input "Enter a string: ";a$
130 gosub 160
140 print b$
150 end
160 rem FUNCTION rot13
170 for i = 1 to len(a$)
180 n = asc(mid$(a$,i,1))
190 e = 255
200 if n > 64 and n < 91 then e = 90 : rem uppercase
210 if n > 96 and n < 123 then e = 122 : rem lowercase
220 if e < 255 then n = n+13
230 if n > e then n = n-26
240 b$ = b$+chr$(n)
250 next
260 return