On May 12, 2012, at 8:35 AM, saad bashir wrote: > Dear Matthias, > > Thank you for replying to me. I am sure this is laughably basic for you.
It is basic for me, but there's nothing laughable. > I got what you wrote. I know string-ith extracts the letter. My question is > how to use it. I have tried various ways of writing both in the def and > interaction sections but have not worked out. Even consulting the Helpdesk > has not helped as it does not tell me how to use the fucntion. > > Sorry if I am being very thick. I really want to do it right. > If you have a DrRacket in front of you, does it say "Welcome to DrRacket, version 5.2.1" Language: Beginning Student. in the Interactions WIndow? If not, you need to switch languages with the Language menu. Once you have switched languages, click run. Then try these interactions: > (string-ith "hello world" 0) "h" > (string-ith "hello world" 1) "e" > (string-ith "hello world" 2) "l" > (string-ith "hello world" 3) "l" > Please let me know which step went wrong previously. -- Matthias > Saad > > On Fri, May 11, 2012 at 11:47 PM, Matthias Felleisen <[email protected]> > wrote: > > The beginning of section 2.1.3 looks like this: > > > > All other operations concerning strings consume or produce data other than > > strings. Here are some examples: > > • string-length consumes a string and produces a (natural) number; > > > > • string-ith consumes a string s and extracts the one-character > > substring located at the ith position (counting from 0); and > > > > • number->string consumes a number and produces a string. > > > > Also look up substring and find out what it does. > > Which function do you think extracts a "letter" from a string? [[You can > follow the links for the function names. Perhaps it is easier to read the > docs.]] > > -- Matthias > > > > > On May 11, 2012, at 4:22 PM, saad bashir wrote: > > > I am back again. I had a basic inquiry and your help got me started. > > > > My problem is as follows: > > > > I have just started to work through 2Htdp (i.e. the second edition) that > > you had guided me to. Having gone through the prologue I am now on the > > second chapter, "Fixed-size data." But have got stuck almost at the start. > > I have successfully done the first two exercises but have hit a road block > > on exercise 3 (section 2.1.3 "Mixing it up"). I do not know what > > instruction to use to insert or extract a letter from the ith position. I > > think I am doing something wrong when trying to look up things in Helpdesk. > > Please help. > > > > Saad > > > > On Fri, Apr 27, 2012 at 8:32 PM, Danny Yoo <[email protected]> wrote: > > On Fri, Apr 27, 2012 at 11:27 AM, saad bashir <[email protected]> wrote: > > > Your help was great. Things are working now. And a great thank you for > > > leading me to the 2d edition of How to Design Programs. I had not known > > > about it. > > > > > > Glad to hear that it's working for you now! Please feel free to > > continue to ask questions on the mailing list; we'll be happy to help. > > > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > >
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