C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Need some pointers          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Heather Guest Posted: Mon Nov 15, 2004 11:39 am    Post subject: Need some pointers I am not asking anyone to write my program for me. I want to get that out upfront. I just desperately need some pointers. C++ is the first language I have ever taken a class in. Up until now I have grasped things rather easily. This time I haven't. Whether it is the concept itself or just trouble concentrating (had a tooth cut out, reacted to the numbing medication, yada yada..been knocked on my butt by medication) I don't know. This is what I was assigned: "Read in a string of maximum 11 characters (including the at the end) and whatever is typed in, reverse it using a function of your own making". I know I need to find the and go backwards from there...I just can not grasp how to do it. I have tried looking online using google, but I am not finding anything that doesn't rely on an outside function. Can someone please help? I don't usually wait until last minute to do programs, but the medication they gave me to counteract the reaction to the numbing medication has kept me knocked out most of the time since Thursday and I just am totally lost and need some pointers. Thanks Heather [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thomas Mang Guest Posted: Mon Nov 15, 2004 9:37 pm    Post subject: Re: Need some pointers "Heather" <hlc101202 (AT) mchsi (DOT) com> schrieb im Newsbeitrag news:0WSld.338164$wV.50567 (AT) attbi_s54 (DOT) .. Quote: I am not asking anyone to write my program for me. I want to get that out upfront. I just desperately need some pointers. C++ is the first language I have ever taken a class in. Up until now I have grasped things rather easily. So you are either a genious or you haven't learnt that much about C++ :-) This time I haven't. Whether it is the concept Quote: itself or just trouble concentrating (had a tooth cut out, reacted to the numbing medication, yada yada..been knocked on my butt by medication) I don't know. This is what I was assigned: "Read in a string of maximum 11 characters (including the at the end) and whatever is typed in, reverse it using a function of your own making". I know I need to find the and go backwards from there...I just can not grasp how to do it. I have tried looking online using google, but I am not finding anything that doesn't rely on an outside function. Can someone please help? I don't usually wait until last minute to do programs, but the medication they gave me to counteract the reaction to the numbing medication has kept me knocked out most of the time since Thursday and I just am totally lost and need some pointers. These terms should help you to build various solutions to your problem: std::strlen loops (for, while) std::string (this class is so heavy; take a close look at everything dealing with reverse_iterator [constructors, member functions returning them]). std::reverse Thomas [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Ivan Vecerina Guest Posted: Mon Nov 15, 2004 9:38 pm    Post subject: Re: Need some pointers "Heather" <hlc101202 (AT) mchsi (DOT) com> wrote Quote: I am not asking anyone to write my program for me. I want to get that out upfront. I just desperately need some pointers. .... don't know. This is what I was assigned: "Read in a string of maximum 11 characters (including the at the end) and whatever is typed in, reverse it using a function of your own making". You could look for inspiration at the implementation of the std::reverse function of the standard library implementation you use (header <algorithm>). Quote: I know I need to find the and go backwards from there...I just can not grasp how to do it. I have tried looking online using google, but I am not finding anything that doesn't rely on an outside function. You swap the first and last character, and go on that way. I think you should just start implementing this and see... Of course, clc++.*moderated* is not a good place to get urgent replies (since every message posted is first reviewed by a moderator). Good luck ;) -- http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top R.F. Pels Guest Posted: Mon Nov 15, 2004 11:17 pm    Post subject: Re: Need some pointers Heather wrote: Quote: I know I need to find the and go backwards from there...I just can not Use a stack. -- Ruurd ..o. ...o ooo [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top M Jared Finder Guest Posted: Tue Nov 16, 2004 11:31 am    Post subject: Re: Need some pointers Heather wrote: Quote: I am not asking anyone to write my program for me. I want to get that out upfront. I just desperately need some pointers. C++ is the first language I have ever taken a class in. Up until now I have grasped things rather easily. This time I haven't. Whether it is the concept itself or just trouble concentrating (had a tooth cut out, reacted to the numbing medication, yada yada..been knocked on my butt by medication) I don't know. This is what I was assigned: "Read in a string of maximum 11 characters (including the at the end) and whatever is typed in, reverse it using a function of your own making". I know I need to find the and go backwards from there...I just can not grasp how to do it. I have tried looking online using google, but I am not finding anything that doesn't rely on an outside function. Can someone please help? I don't usually wait until last minute to do programs, but the medication they gave me to counteract the reaction to the numbing medication has kept me knocked out most of the time since Thursday and I just am totally lost and need some pointers. It's perfectly okay to use outside functions, as long as you also implement those functions. You may have seen a solution along the lines of this: void reverse_string( char* string ) { reverse( string, string + strlen( string )); } reverse and strlen are both standard library functions. If you can implement a my_reverse and my_strlen, then you can write your solution using those instead of the standard ones. To implement them, you'll need to use looping and feel somewhat comfortable with pointers. -- MJF [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Michiel Salters Guest Posted: Wed Nov 17, 2004 2:12 am    Post subject: Re: Need some pointers "Heather" <hlc101202 (AT) mchsi (DOT) com> wrote Quote: I am not asking anyone to write my program for me. I want to get that out upfront. I just desperately need some pointers. C++ is the first language I have ever taken a class in. Up until now I have grasped things rather easily. This time I haven't. Whether it is the concept itself or just trouble concentrating (had a tooth cut out, reacted to the numbing medication, yada yada..been knocked on my butt by medication) I don't know. This is what I was assigned: "Read in a string of maximum 11 characters (including the at the end) and whatever is typed in, reverse it using a function of your own making". That question is a giveaway. You have a bad C++ class. Usually, we don't bother with or maximum string lengths. It's only when you have to interface with C code, that you need to use char const* instead of std::string. Quote: I know I need to find the and go backwards from there...I just can not grasp how to do it. I have tried looking online using google, but I am not finding anything that doesn't rely on an outside function. Can you create a pointer to the '' character, given a char const* to the first char? That is really easy; just look at the first char (*pointer). If that is =='', you found it. If not, move the pointer to the next char (pointer++) until you have the ''. Now, go back one (pointer--) and you have the last character. Regards, Michiel Salters [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Allan W Guest Posted: Thu Nov 18, 2004 12:27 am    Post subject: Re: Need some pointers Quote: Heather wrote: I am not asking anyone to write my program for me. I want to get that out upfront. I just desperately need some pointers. M Jared Finder <mfinder (AT) digipen (DOT) edu> wrote Quote: It's perfectly okay to use outside functions, as long as you also implement those functions. Not neccesarily. If this is an instructor-led class, it may depend on the instructor and/or on the purpose of the lesson. If the purpose is to get some experience with pointer variables, the instructor might be asking for students to do it all in one function without using any "outside functions" at all. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Allan W Guest Posted: Thu Nov 18, 2004 12:41 am    Post subject: Re: Need some pointers Quote: "Heather" <hlc101202 (AT) mchsi (DOT) com> schrieb C++ is the first language I have ever taken a class in. Up until now I have grasped things rather easily. "Thomas Mang" <nospam (AT) nospam (DOT) invalid> wrote Quote: So you are either a genious or you haven't learnt that much about C++ Not sure it needs to be either one of those extremes. Quote: This is what I was assigned: "Read in a string of maximum 11 characters (including the at the end) and whatever is typed in, reverse it using a function of your own making". To find the , use strlen to find the length of the string, and then use pointer arithmetic: the expression p + std::strlen(p) will give you a pointer to the . I notice that most of the answers you've gotten so far have focused on how to reverse the string in memory. If the above quote is accurate, this might be more than you need. When the assignment says to "reverse it" this could be interpreted as "print it out in reverse." If so, your task can be made much simpler: print out the last character (NOT including the ), then the previous one, and so on until you've printed out the very first character. You could do this by using a for loop, where you start out by initializing a pointer q to the character, and you continue while q>p. Remember that q needs to move backwards instead of forwards. Good luck. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top M Jared Finder Guest Posted: Sat Nov 20, 2004 4:20 pm    Post subject: Re: Need some pointers Allan W wrote: Quote: Heather wrote: I am not asking anyone to write my program for me. I want to get that out upfront. I just desperately need some pointers. M Jared Finder <mfinder (AT) digipen (DOT) edu> wrote It's perfectly okay to use outside functions, as long as you also implement those functions. Not neccesarily. If this is an instructor-led class, it may depend on the instructor and/or on the purpose of the lesson. If the purpose is to get some experience with pointer variables, the instructor might be asking for students to do it all in one function without using any "outside functions" at all. I've had classes like that; they were all awful because they encouraged the use of bad habits. If you want to get students familiar with pointers, give an assignment like "reverse a singlely linked list", which can't be done with out pointers. But don't impose an artificial restriction that would cause students to learn bad style. -- MJF [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Gary Labowitz Guest Posted: Sun Nov 21, 2004 4:59 am    Post subject: Re: Need some pointers "M Jared Finder" <mfinder (AT) digipen (DOT) edu> wrote < Quote: I've had classes like that; they were all awful because they encouraged the use of bad habits. If you want to get students familiar with pointers, give an assignment like "reverse a singlely linked list", which can't be done with out pointers. But don't impose an artificial restriction that would cause students to learn bad style. Good idea in theory, very hard in practice. The assignment you suggest (good one!) involves the student learning what a linked list is. They have enough trouble remembering what a variable is. It would take a week to study linked list enough to understand what reversing a singlely linked list entails. It's hard enough just getting the idea of passing a pointer to a function, which is a more useful idea to conquer. (Of course I teach them pass by reference first, and remind them to use it whenever possible.) -- Gary [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Allan W Guest Posted: Mon Nov 22, 2004 11:06 pm    Post subject: Re: Need some pointers Quote: M Jared Finder <mfinder (AT) digipen (DOT) edu> wrote It's perfectly okay to use outside functions, as long as you also implement those functions. Allan W wrote: Not neccesarily. If this is an instructor-led class, it may depend on the instructor and/or on the purpose of the lesson. If the purpose is to get some experience with pointer variables, the instructor might be asking for students to do it all in one function without using any "outside functions" at all. M Jared Finder <mfinder (AT) digipen (DOT) edu> wrote Quote: I've had classes like that; they were all awful because they encouraged the use of bad habits. Which bad habits are you referring to? I think it's very instructive to ask students to write their own version of std::strcpy(). That doesn't mean that I would advise them not to use the library version... as a matter of fact, it's a good opportunity to lecture on the difference between system-dependant code (often written in assembly language) and portable code, and when each one is appropriate. Quote: If you want to get students familiar with pointers, give an assignment like "reverse a singlely linked list", which can't be done with out pointers. But don't impose an artificial restriction that would cause students to learn bad style. Still not sure what "bad style" you're talking about. Perhaps you mean, "use library code whenever it is helpful?" But you can't introduce the entire standard library at once. Also, I agree with Gary Labowitz -- talking about a linked list is rather an advanced topic. As far as beginners are concerned, the sole purpose of a pointer is to support "new T" -- and if my school allowed it, I would talk about smart pointers in the very next lesson. (Alas, I've got quite a few topics to talk about in an 8-week class, but smart pointers are not on that list. I do encourage students to look it up on their own after class has ended.) [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top M Jared Finder Guest Posted: Sun Nov 28, 2004 11:38 am    Post subject: Re: Need some pointers Allan W wrote: Quote: Allan W wrote: Not neccesarily. If this is an instructor-led class, it may depend on the instructor and/or on the purpose of the lesson. If the purpose is to get some experience with pointer variables, the instructor might be asking for students to do it all in one function without using any "outside functions" at all. M Jared Finder <mfinder (AT) digipen (DOT) edu> wrote I've had classes like that; they were all awful because they encouraged the use of bad habits. Which bad habits are you referring to? Putting way too much code into one function. I have seen way too many functions that span two to three pages but could be reduced to a few lines if common functionality was separated out. Quote: I think it's very instructive to ask students to write their own version of std::strcpy(). That doesn't mean that I would advise them not to use the library version... as a matter of fact, it's a good opportunity to lecture on the difference between system-dependant code (often written in assembly language) and portable code, and when each one is appropriate. I agree; in fact I think its important to get the students to think in such a way that would get them to write those functions. The original poster's question was how to reverse a C-string. By realizing you can implement that as reverse(cstr, cstr + strlen(cstr)), a student starts to practice and learn about abstraction, which I view as *the* fundamental skill in computer programming. -- MJF [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Greg Comeau Guest Posted: Sun Nov 28, 2004 11:53 pm    Post subject: Re: Need some pointers In article <30sj4tF33aro8U1 (AT) uni-berlin (DOT) de>, M Jared Finder <mfinder (AT) digipen (DOT) edu> wrote: Quote: Allan W wrote: I've had classes like that; they were all awful because they encouraged the use of bad habits. Which bad habits are you referring to? Putting way too much code into one function. I have seen way too many functions that span two to three pages but could be reduced to a few lines if common functionality was separated out. I think it's very instructive to ask students to write their own version of std::strcpy(). That doesn't mean that I would advise them not to use the library version... as a matter of fact, it's a good opportunity to lecture on the difference between system-dependant code (often written in assembly language) and portable code, and when each one is appropriate. I agree; in fact I think its important to get the students to think in such a way that would get them to write those functions. The original poster's question was how to reverse a C-string. By realizing you can implement that as reverse(cstr, cstr + strlen(cstr)), a student starts to practice and learn about abstraction, which I view as *the* fundamental skill in computer programming. I've historically taught C++ to C programmers. Early on I realized that they thought C++ was going to give them abstraction, when actually it is they who need to give it to themselves. So while they are being teased with classes, I try to hit home that abstraction has been in their ability/touch all along. One way to do that is actually to have them design and write a reverse function. Indeed, the example can cover so many fundamental aspects to programming involving design, knowledge, creativity, organization, documentation, commonality, seperation, delegation, abstraction, making compromises, mainline code vs library code, efficiency, etc. And what starts out as "Why the hell are we doing this?" protests becomes a sense of calmness as each absorbs the insights until eventually they're blurting "Can we do another like this?" as many of the students, who include existing programmers, have never seen anything like that before or realized the numerous abstraction mechanism availablr. -- Greg Comeau / Comeau C++ 4.3.3, for C++03 core language support Comeau C/C++ ONLINE ==> http://www.comeaucomputing.com/tryitout World Class Compilers: Breathtaking C++, Amazing C99, Fabulous C90. Comeau C/C++ with Dinkumware's Libraries... Have you tried it? 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