How to get variable length array

Asked Mar 11 '21 at 17:06

Active Mar 11 '21 at 17:11

Viewed 116 times

I know variable length arrays are not allowed in c++. My code is currently as follows:

int main(){
  int t;
  cin >> t;
  double h[t];
}

How can I create an array with length t then?

Edit: the assignment only allows char, bool, int and double. Vector isn't allowed. When I tried to compile it, it says ISO C++ forbids variable length array 'h'.

edited Mar 11 '21 at 17:10

asked Mar 11 '21 at 17:06

throwaway

7

Use `std::vector h(t);`. (And, don't forget to `#include ` before.) – Scheff's Cat Mar 11 '21 at 17:07
2

I'm sure searching could've revealed this. – underscore_d Mar 11 '21 at 17:08
What's wrong with your code? It does create an array with length t. – Wais Kamal Mar 11 '21 at 17:09
1

Any [good C++ book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) should cover this. – Lukas-T Mar 11 '21 at 17:09
1

g++ will allow this with the right compile options. It is not standard C++, though. – Fred Larson Mar 11 '21 at 17:09
3

If you can't use `vector`, then search about `new[]`. – underscore_d Mar 11 '21 at 17:10
4

An alternative would be to use `double *h = new double[t];`. (A proper program should `delete[] h;` after you don't need `h` anymore.) – Scheff's Cat Mar 11 '21 at 17:10
1

And to be tidy, use `delete [] h;` when you're done. – Fred Larson Mar 11 '21 at 17:11
***it says ISO C++ forbids variable length array 'h'*** This is correct. VLAs are not part of standard c++. Related: [https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard) – drescherjm Mar 11 '21 at 17:11
1

@WaisKamal To quote from the question _"variable length arrays are not allowed in c++"_. That's wrong, it's non-standard C++. – Lukas-T Mar 11 '21 at 17:11
`new double[t]` how about that. You can use a smart pointer for extra kicks. – user1095108 Mar 11 '21 at 17:12
5

...and you may send your teacher the following link: [Kate Gregory: Stop Teaching C](https://www.youtube.com/watch?v=YnWhqhNdYyk)... ;-) – Scheff's Cat Mar 11 '21 at 17:13

How to get variable length array

0 Answers0