Iterate through characters of a string?

Code:
dim printwidth=28



Let a$="PART 1 Bruce Hall, a slightly built youth 16 years of age, fair haired and blue eyed, stood 4' 8 in shoes and despite that slight assistance still could not see over the brick wall behind which he believed stood a flying machine. At least that was what he'd overheard two delivery boys discussing outside the local butchers shop."



REM pRINT a(1 to 10)

dim stringpos as integer

stringpos=0

dim lines as integer

dim sentenceEnd as integer

while stringpos<len(a)

sentenceEnd=stringpos+printwidth



if sentenceEnd<len(a) then



FOR stringposIter=sentenceEnd TO stringpos STEP -1

if code(a(stringposIter to stringposIter))=code(" ") then



print at lines,0;a(stringpos to stringposIter)



stringpos=stringposIter

exit for

end if

next



end if



if sentenceEnd>len(a) then

print at lines,0;a(stringpos to sentenceEnd)

exit while

end if



lines=lines+1



wend