Dear Matthias, This is what I needed. I did not understand how to use string-ith. Now I do. Thank you very much.
Laurent also sent me links to some beginner's intro videos on You Tube. I am amazed and eternally grateful that people of your calibre would take the time and trouble to help a tyro like me who must seem like an annoying gnat to you. Thank you guys. Saad PS I will probably trouble you again. Will try to keep it to minimum. On Sat, May 12, 2012 at 4:40 PM, Matthias Felleisen <[email protected]>wrote: > > 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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