How can I create an array in C++ with its lenght equals to user input?

Question

I know I can't create arrays like this:

int main () {
    int length;
    std::cin >> length;
    int array [length] = {};
}

Is there any way I can do it?

you can do it for some compilers – Bryan Chen Mar 04 '14 at 22:13 — Bryan Chen, Mar 04 '14 at 22:13
And spellcheck your variable names! – Mats Petersson Mar 04 '14 at 22:15 — Mats Petersson, Mar 04 '14 at 22:15
I'm sorry !!! I'm not a native speaker ... – matheussilvapb Mar 04 '14 at 22:21 — matheussilvapb, Mar 04 '14 at 22:21

score 7 · Answer 1 · answered Mar 04 '14 at 22:13

7

Use a vector:

std::vector<int> arr(length);

This will contain length value-initialized int's.

answered Mar 04 '14 at 22:13

Luchian Grigore

Marius Bancila · Answer 2 · 2014-03-04T22:24:35.950

2

There are several options. You can use an STL container such as std::vector:

int lenght;
std::cin >> length;
std::vector<int> arr(length);

Or you can allocate memory dynamically:

int* arr = new int[length];

edited Mar 04 '14 at 22:24

answered Mar 04 '14 at 22:15

Marius Bancila

By using `std::vector` in this case one does allocate memory dynamically too. – lapk Mar 04 '14 at 22:16
2

`std::array` doesn't work. The length is a template parameter and therefore must be a compile time constant. `std::array` is a completely separate type from `std::array`. Hiding it in a `shared_ptr` doesn't make that go away (and wouldn't make much sense even if it worked). – Mar 04 '14 at 22:18
Good point, thanks for the correction. – Marius Bancila Mar 04 '14 at 22:25

score 1 · Accepted Answer · answered Mar 04 '14 at 22:14

1

Use vector

#include <vector>

int main() {
  int length;
  std::cin >> length;
  std::vector<int> dynamic_array(length); 
}

answered Mar 04 '14 at 22:14

Blaz Bratanic

3 Answers3