Function Rot13$(t$)
    for i = 1 to len(t$)
        ch$=mid$(t$,i,1)
        if (asc(ch$)>=asc("A")) and (asc(ch$)<=asc("Z")) then
            ch$=chr$(asc("A")+ (asc(ch$)-asc("A")+13) mod 26)
        end if
        if (asc(ch$)>=asc("a")) and (asc(ch$)<=asc("z")) then
            ch$=chr$(asc("a")+ (asc(ch$)-asc("a")+13) mod 26)
        end if
        Rot13$=Rot13$+ch$
    next
    end function