#define FAIL -1

sub mtf( s() as string, i as uinteger )
    'moves the symbol at index i to the front and shifts preceding ones back
    dim as string*1 t = s(i)
    for j as uinteger = i to 1 step -1
        s(j) = s(j-1)
    next j
    s(0)=t
end sub

sub make_symbols( s() as string )
    'populates an array of strings with the lowercase alphabet
    for i as uinteger = 97 to 122
        s(i-97) = chr(i)
    next i
end sub

function find( s() as string, l as string ) as integer
    'returns the index of the first occurrence of the symbol l in s()
    for i as uinteger = 0 to ubound(s)
        if s(i) = l then return i
    next i
    return FAIL
end function

sub encode( s() as string, ind() as uinteger )
    dim as integer n = ubound(s), i
    redim as uinteger ind(0 to n)
    dim as string a(0 to 25)
    make_symbols(a())
    for z as uinteger = 0 to n
        i = find( a(), s(z) )
        if i = FAIL then
            print "Uh oh! Couldn't find ";s(z);" in alphabet."
            end
        end if
        mtf( a(), i )
        ind(z) = i
    next z
end sub

sub decode( s() as string, ind() as uinteger )
    dim as integer n = ubound(ind), i
    redim as string s(0 to n)
    dim as string a(0 to 25)
    make_symbols(a())
    for z as uinteger = 0 to n
        s(z) = a(ind(z))
        mtf(a(), ind(z))
    next z
end sub

sub printarr( s() as string )
    for i as uinteger = 0 to ubound(s)
        print s(i);
    next i
    print
end sub

sub printind( ind() as integer )
    for i as uinteger = 0 to ubound(ind)
        print ind(i);" ";
    next i
    print
end sub

sub compose( s() as string, b as string )
    'turns a string into a zero-indexed array of single letters
    'The reason we use such arrays is to get them zero-indexed
    'and to make the point that we could work with multi-char
    'symbol tables if we wanted to
    dim as integer n = len(b), i
    redim as string s(0 to n-1)
    for i = 0 to n-1
        s(i) = mid(b, 1+i, 1)
    next i
end sub

'-----------now the tests-------------
redim as string s(0)
redim as integer ind(0)

compose( s(), "broood" )
encode( s(), ind() )
printind( ind() )
decode( s(), ind() )
printarr( s() ) : print

compose( s(), "bananaaa" )
encode( s(), ind() )
printind( ind() )
decode( s(), ind() )
printarr( s() ) : print

compose( s(), "hiphophiphop" )
encode( s(), ind() )
printind( ind() )
decode( s(), ind() )
printarr( s() )