c++ - Overloading operator trouble -


hello i'm trying create program reads in series of infix expressions file until reaches semi-colon or period (a+b.), , output postfix of expression file. i'm having trouble getting overloaded operators work correctly. can give me tips on what's wrong them?

std::istream& operator>>(std::istream& in, expression& x) {     char y;     {         in >> y;         x.ifix += y;         if (y == '.') {             x.last = true;         }     } while (y!= ';' || y!= '.');     x.converttopostfix();      return in; }  std::ostream& operator<<(std::ostream& out, const expression& x) {     out << x.pfix;      return out; }

this expression true:

while (y != ';' || y != '.');

if y ';' , y can not '.', second half true. same other way around when y '.'.

you want 

while (y != ';' && y != '.');

or, if want express more human:

while (!(y == ';' || y == '.'));

in other words, "do stuff while y not equal semicolon or dot".

this common mistake when combining conditions, , 1 worth spending time understand, can spot in future - because make mistake again, guarantee it.


Comments

Post a Comment

Popular posts from this blog

android - Get AccessToken using signpost OAuth without opening a browser (Two legged Oauth) -

i using signpost oauth access data magento server. have read various tutorials on same , reach point open browser user can enter credentials. however, per requirement have automate part. hence, user should not browser page. have set-up done on server side ( magento ), hit url , returned call page. same through program in android. i have tried below, consumer = new commonshttpoauthconsumer(key, secret); provider = new commonshttpoauthprovider(oauth_init_url,access_token_url, authorize_url); try { provider.retrieverequesttoken(consumer, oauth.out_of_band); log.d("tokens" , consumer.gettoken() + " -- " + consumer.gettokensecret()); } and request tokens. dont know how bypass next step. tried directly accessing accesstoken (stupid of me) provider.retrieveaccesstoken(consumer, "mycallback://callback"); no luck, ends in oauth.signpost.exception.oauthnotauthorizedexception: authorization failed (server replied 401). ...
Read more

org.mockito.exceptions.misusing.InvalidUseOfMatchersException: mockito -

getting error org.mockito.exceptions.misusing.invaliduseofmatchersexception: invalid use of argument matchers! 1 matchers expected, 2 recorded. exception may occur if matchers combined raw values: //incorrect: somemethod(anyobject(), "raw string"); when using matchers, arguments have provided matchers. example: //correct: somemethod(anyobject(), eq("string matcher")); at when( getprogramservice .callservice(any(getprogramtype.class))) .thenreturn(jaxbresponse); please explain error , possible resolution the code posted looks fine; don't see problem it. code before or above causing exception. key here: invalid use of argument matchers! 1 matchers expected, 2 recorded. any , used above, doesn't return "special kind of null" or "special kind of getprogramtype"; don't exist. instead, returns null , side effect puts matcher on stack. whe...
Read more

google shop client API returns 400 bad request error while adding an item -

i'm working on solution add items in google shopping market java application. following tutorial real mess because of missing classes of laste release, after setting 1.5-beta maven managed make base example typecheck correctly classes. still can make simple task of adding 1 item. instead of posting whole code i'm posting part creates product feed. private product createproduct(string id) { product product = new product(); product.title = "red wool sweater"; product.content = new content( "text", "comfortable , soft, sweater keep warm on " + "cold winter nights. red , blue stripes."); product.appcontrol = new appcontrol(); product.appcontrol.addrequireddestination("productads"); product.externalid = id; product.lang = "it"; product.country = "it"; product.condition = "nuovo"; product.price = new price("eu...
Read more