@programminginc - страница 3172

Tomay

I am new here,

Tomay

But I have one question for the moment,

Tomay

I don't get the differences between auto, auto& and auto&&, and what it is used for for loop iterators? Can you explain it to me in a more easy way (Because I don't get the cppreference.com web ones).

Mar!o

auto&& allows perfect forwarding for example consider: #include <vector> int main() { std::vector<bool> v(10); for (auto& e : v) e = true; } This doesn't compile because rvalue vector<bool>::reference returned from the iterator won't bind to a non-const lvalue reference. But this will work: #include <vector> int main() { std::vector<bool> v(10); for (auto&& e : v) e = true; }

Mar!o

auto& is just a reference while only auto is working with copies

Anonymous

How to insertion and deleting operation in "linked list" using 'c'

Anonymous

How to insertion and deleting operation in "linked list" using 'c'

Help me plz

Anonymous

How to insertion and deleting operation in "linked list" using 'c'

google the sentence

Anonymous

I don't get the differences between auto, auto& and auto&&, and what it is used for for loop iterators? Can you explain it to me in a more easy way (Because I don't get the cppreference.com web ones).

you won't really use auto && inside a for loop. either auto is used or auto &. auto when the type is small and copying is better (example - built-in types such as int, float), auto & when the type is larger (example - std::vector).

Anonymous

you might also use const auto & sometimes to avoid accidentally changing the value

Tomay

I lost internet for an hour.

Anonymous

auto&& allows perfect forwarding for example consider: #include <vector> int main() { std::vector<bool> v(10); for (auto& e : v) e = true; } This doesn't compile because rvalue vector<bool>::reference returned from the iterator won't bind to a non-const lvalue reference. But this will work: #include <vector> int main() { std::vector<bool> v(10); for (auto&& e : v) e = true; }

oh so there is actually an use for auto &&.

Tomay

Thank you guys for the answers, but could you please agree on something!

Tomay

Here is what I understood: 1 - To deal with types by copy, like the small ones : bool, int, float, double... I simply use "auto". 2 - To deal with types by reference, like the ones std::string, std::vector... I should use "auto&", but if the compiler complains about it, then I should use "const auto&" UNLESS I want to modify the reference content, then in this case I should finally use "auto&&". @pinsrq and @chandradeepdey, correct me please I am wrong.

Jaime

Good night

Anonymous

I don't get the differences between auto, auto& and auto&&, and what it is used for for loop iterators? Can you explain it to me in a more easy way (Because I don't get the cppreference.com web ones).

If you are familiar with templates, then this would be a perfect analogy template<typename T> void fun(T param) The deduction of type of param based on some argument to fun would be what is deduced by auto a = arg; //auto deduces the same type //as deduced for param when //called like fun(arg) template<typename T> void fun(T& param) auto& a = arg; //auto deduces the same type //as deduced for param when //called like fun(arg) template<typename T> void fun(T&& param) auto&& a = arg; //auto deduces the same type //as deduced for param when //called like fun(arg) The last case is when perfect forwarding happens. There is one scenario where auto and template type deduction differs. It is when you pass a braced initializer list but that is a corner case.

Anonymous

Here is what I understood: 1 - To deal with types by copy, like the small ones : bool, int, float, double... I simply use "auto". 2 - To deal with types by reference, like the ones std::string, std::vector... I should use "auto&", but if the compiler complains about it, then I should use "const auto&" UNLESS I want to modify the reference content, then in this case I should finally use "auto&&". @pinsrq and @chandradeepdey, correct me please I am wrong.

The usage for auto and auto& is almost correct. The usage for auto&& is not when you want to deal with what is left. It is used when you want perfect forwarding. Like for example if you write a function that passes it's arguments to some other functions and you want to preserve the type information, then you use auto&&. So when called with an lvalue auto&& will deduce a lvalue type and a rvalie type otherwise.

Vikas

How to sort an array in descending order?

Apk

How to sort an array in descending order?

a simple google search would answer that

Vikas

a simple google search would answer that

Thanks, I found this on Google sort(arr, arr + n, greater<int>());

king king

Hello dear friends. I'm working with c for about 5 months. And I'm looking for recommendations to a good book for advanced/intermidate (Only C(89), not C++)

ꍏꈤꀸ

Can somebody add me to English chats about WinAPI?

P

Hello guys , I got stuck with a question The problem follows like this given an array of numbers, for example a[]=[ 24, 67, 90, 8 ]we need to find the sum of the numbers in a array which are obtained by multiplying the digits[ 2*4, 6*7,9*0, 8] the result should be 58 (8+42+0+8=58)

Kishan

https://www.hackerrank.com/challenges/crush/problem?h_r=next-challenge&h_v=zen&h_r=next-challenge&h_v=zen

Kishan

https://www.hackerrank.com/challenges/crush/problem?h_r=next-challenge&h_v=zen&h_r=next-challenge&h_v=zen

I wrote a solution for that and it gave me some points, but few testcase, testcase 7 to 13 are failing due to TLE

Kishan

long arrayManipulation(int n, vector<vector<int>> queries) { vector<long> arr(n); long maxe=INT_MIN; long qsize=queries.size(); for(long i=0; i<qsize; i++) { for(long j=queries[i][0]; j<=queries[i][1]; j++) { arr[j-1]+= queries[i][2]; maxe=max(maxe, arr[j-1]); } } return maxe; }

Kishan

long arrayManipulation(int n, vector<vector<int>> queries) { vector<long> arr(n); long maxe=INT_MIN; long qsize=queries.size(); for(long i=0; i<qsize; i++) { for(long j=queries[i][0]; j<=queries[i][1]; j++) { arr[j-1]+= queries[i][2]; maxe=max(maxe, arr[j-1]); } } return maxe; }

This is the code snippet I wrote, any idea how can I further optimize it to get full points

Anonymous

Goodday Esteemed members anyone who is good at c++ kindly inbox

klimi

Goodday Esteemed members anyone who is good at c++ kindly inbox

read rules, thanks

Kishan

This is the code snippet I wrote, any idea how can I further optimize it to get full points

JUST AN UPDATE: Got the solution.

Anonymous

cpp has different stl (header name)

Anonymous

which to learn

Anonymous

msvc or gcc

Mar!o

gcc

Anonymous

why

Anonymous

should I build unix like environment in windows

Anonymous

or change a plateform directly

ꍏꈤꀸ

Can ODBC be used without a DB connection? (I need to operate over .mdb files without connection and even installation of a DB)

olli

msvc or gcc

It shouldn't matter, ideally your code is standard c++ so it can be compiled using different compilers

Ojong

JUST AN UPDATE: Got the solution.

Can u Share?

Kishan

Can u Share?

you want code or logic?

Ojong

you want code or logic?

The code 🙏

Anonymous

anyone needs help in c/c++ write me dm

ꍏꈤꀸ

anyone needs help in c/c++ write me dm

we have a whole group for it)

Tomay

@SilhouetteInDark I just realized that my problem is with "Forwarding References" which is new to me and not with "auto" itself. I have to dig a little bit more.

Anonymous

Please can someone explain the logic of this code to me? //convert a string to integer //ex. String “ryutfg477” //returns 477 int main(char *s) { unsigned int num = 0; s = “good89” while (*s++) { if (*s >= ‘0’ && *s <= ‘9’) num=(num*10) + (*s-‘0’); else if(num > 0) break; } return (num); }

Vikas

How to initialize 2d array in c++ with 1?