C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  can any one help me...          C++Talk.NET Forum Index -> C Language (Moderated) View previous topic :: View next topic   Author Message Guest Posted: Mon Apr 16, 2007 8:18 pm    Post subject: can any one help me... hi 4nds... if i declare int a=10; the value 10 will be assigned in a; similarly if i declare void main() { int a,b=10; a=&b; } why can't the variable store the address the address of variable be just like storing a int value..?? why shud a be a pointer variable?? pls answer me.... -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Martin Ambuhl Guest Posted: Thu Apr 19, 2007 7:13 pm    Post subject: Re: can any one help me... madhuriIST (AT) gmail (DOT) com wrote: Quote: hi 4nds... if i declare int a=10; the value 10 will be assigned in a; similarly if i declare void main() ^^^^ This is an error that *no* competent C textbook or instructor teaches. Quote: { int a,b=10; a=&b; ^^^^ This is very dangerous. &b yields an address; it should be stored in a pointer. a is an int, not a pointer. Conversion between ints and pointers makes non-portable programs and the use of such conversions requires a knowledge of the particular implementation that, frankly, you are very unlikely to have. Quote: } why can't the variable store the address the address of variable be just like storing a int value..?? It can: int main(void) { int *a; /* a is a pointer-to-int */ int b = 10; /* b is an int */ b = &a; /* a now points to b */ return 0; } Quote: why shud a be a pointer variable?? It *should* because you are trying to store a pointer value in it. Quote: pls answer me.... *Please* don't whine. -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top John Dallman Guest Posted: Thu Apr 19, 2007 7:13 pm    Post subject: Re: can any one help me... In article <clcm-20070416-0043 (AT) plethora (DOT) net>, madhuriIST (AT) gmail (DOT) com () wrote: Quote: void main() { int a,b=10; a=&b; } why can't the variable store the address the address of variable be just like storing a int value..?? why shud a be a pointer variable?? Because C, while not a fully type-safe language, distinguishes clearly between integer types and pointer types. If you want a language that doesn't, you want assembler, or BCPL. In general, trying to store pointers and ints in the same variables is a bad idea: how will functions to which they are passed know what kind of data they've received? If you really want to do this, look up C "union", which will let you do it, but makes you spell out that this is really what you want. It's a good idea to learn the basics of C thoroughly before trying to get clever, though: getting exactly what you ask for, when you don't know clearly what you want or why, leads to trouble. This is as true in programming as it is in stories. -- John Dallman, jgd (AT) cix (DOT) co.uk, HTML mail is treated as probable spam. -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Keith Thompson Guest Posted: Thu Apr 19, 2007 7:14 pm    Post subject: Re: can any one help me... madhuriIST (AT) gmail (DOT) com writes: Quote: hi 4nds... I think "4nds" is supposed to be "friends". The time I and others wasted figuring that out vastly exceeds the time it would have taken you to spell out the word. This is not a chat room. *Please* take the time to spell out words rather than using silly abbreviations like "shud" and "pls". We don't worry about minor errors in grammar and spelling, especially if English isn't your first language, but deliberate obfuscation is not welcome. Quote: if i declare int a=10; the value 10 will be assigned in a; Right. Quote: similarly if i declare void main() The main returns int, not void. If you have a book that says main returns void, get rid of it. The correct declaration is int main(void) Quote: { int a,b=10; a=&b; } why can't the variable store the address the address of variable be just like storing a int value..?? Because integers and pointers are two different things. They *might* have similar representations on some systems; on others, there may not even be an integer type big enough to hold a pointer value. Quote: why shud a be a pointer variable?? Because you want to store a pointer value (an address) in it. Why would you think it shouldn't be a pointer variable? Quote: pls answer me.... I just did. (Asking the question is sufficient; requesting that we answer it is redundant.) -- Keith Thompson (The_Other_Keith) kst-u (AT) mib (DOT) org <http://www.ghoti.net/~kst> San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst> "We must do something. This is something. Therefore, we must do this." -- Antony Jay and Jonathan Lynn, "Yes Minister" -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Douglas A. Gwyn Guest Posted: Thu Apr 19, 2007 7:14 pm    Post subject: Re: can any one help me... madhuriIST (AT) gmail (DOT) com wrote: Quote: if i declare int a=10; the value 10 will be assigned in a; similarly if i declare void main() { int a,b=10; a=&b; } Actually that is wrong and should generate a diagnostic. I presume you meant int *a, b = 10; Quote: why can't the variable store the address the address of variable be just like storing a int value..?? There are ways to do that, such as: uintptr_t aa; aa = (uintptr_t)&b; but there is rarely any good reason for doing that. Quote: why shud a be a pointer variable?? Because you're assigning an address to it. Addresses in C are an abstraction, not necessarily represented the same as integers. The "same" location may have its address represented differently depending on the type of the object that is presumed to be at that location. One advantage of this scheme is that pointer arithmetic, which knows the byte-width of the pointed-to object, automatically scales by that width. For example: double x[10], *p = x; while (p < &x[10]) *p++ = 0.0; If you were using plain integers you'd have to deal with the element width somehow: double x[10]; uintptr_t i = (uintptr_t)x; for (; i < sizeof x; i += sizeof(double)) *(double *)i = 0.0; Of course, you can also use array indexing: double x[10]; int i = 0; for (; i < 10; ++i) x[i] = 0.0; but in C that is defined in such a way as to exploit the properties of pointer arithmetic! -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top Jack Klein Guest Posted: Thu Apr 19, 2007 7:15 pm    Post subject: Re: can any one help me... On 16 Apr 2007 15:18:36 GMT, madhuriIST (AT) gmail (DOT) com wrote in comp.lang.c.moderated: Quote: hi 4nds... 4nds doesn't post here anymore, he had a birthday recently, so now he calls himself 5nds. Quote: if i declare int a=10; the value 10 will be assigned in a; No, 'a' will be initialized with the value 10. This is not the same thing as assignment. Quote: similarly if i declare void main() The only portable return type for main() in C is int, not void. Quote: { int a,b=10; a=&b; If you are using an actual C compiler, it must issue a diagnostic at the line above, because it is not valid. If the compiler produces an executable after issuing the diagnostic, executing the code produces undefined behavior. Quote: } why can't the variable store the address the address of variable be just like storing a int value..?? why shud a be a pointer variable?? pls answer me.... u shud reed a buk on see programming. -- Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://c-faq.com/ comp.lang.c++ http://www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c++ http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html -- comp.lang.c.moderated - moderation address: clcm (AT) plethora (DOT) net -- you must have an appropriate newsgroups line in your header for your mail to be seen, or the newsgroup name in square brackets in the subject line. Sorry. Back to top        C++Talk.NET Forum Index -> C Language (Moderated) All times are GMT Page 1 of 1 Powered by phpBB © 2001, 2006 phpBB Group