# rot13.bas
# basic256 1.1.4.0

iOffset = 13

input "> ", str$

str$ = upper(str$)          # a bit of a cheat however old school encryption is always upper case
len = length(str$)

for i = 1 to len
    iTemp =  asc(mid(str$,i,1))

    if iTemp > 64 AND iTemp < 91 then
        iTemp = ((iTemp - 65) + iOffset) % 26
        print chr(iTemp + 65);
    else
        print chr(iTemp);
    end if

next i