What is the best way to declare an array in C++?

Question

I was curious as to what will be a better way to initalise an array in C++?

Will it be:

int array[50];

or

int x;

cin>> x; //Input a number to initialise the array.

int array[x];

Which of these two will be a better option to initialise an array and why? If none, then is there a third way?

The first is valid C++, the second isn't. So the first one is the best out of the two. — juanchopanza
– juanchopanza, Commented Feb 5, 2016 at 8:10
Neither initialises the array. int array[50] = {0}; would be the best way to initialise it, if you really need an array. — molbdnilo
– molbdnilo, Commented Feb 5, 2016 at 8:15

Humam Helfawi · Accepted Answer · 2017-02-12 13:08:57Z

9

If you want a static array(const number of items), use std::array:

std::array<int,50> a;

If you want a dynamic array(non const number of array), use std::vector:

std::vector<int> a(50);

in this case you can change the size of the vector any time you want by resizing it:

a.resize(100);

or just by pushing new items:

a.push_back(5);

read more about std::vector. It can serve you more than you can imagine.

P.S. the second code of your question is not valid (or at least it is not standard). However, you can do this instead:

int x;
cin>> x; //Input a number to initialise the array.
std::vector<int> array(x);

edited Feb 12, 2017 at 13:08

answered Feb 5, 2016 at 8:11

Humam Helfawi

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6 Comments

Kartik Sibal Over a year ago

What if i declare namespace stds before main? How will this work in that case?

Humam Helfawi Over a year ago

you mean using namespace std; ??

Kartik Sibal Over a year ago

Yes. I am a newbie so. :-)

Humam Helfawi Over a year ago

it is not best practise to using the whole std namespace just write it in front of every thing you would use like std::vector... std::array ... std::sort ... but if there is something you will use a lot like std::begin for example then just use it : using std::begin. and try to make inside a specific method .

Kartik Sibal Over a year ago

It'd be lovely if you could elaborate as to why it isn't a good practise.

|

Daniel · Accepted Answer · 2016-02-05 08:13:12Z

2

If you know the size of an array at compile time, and it will not change, then the best way is:

std::array<int, 50> arr;

Otherwise use

std::vector<int> arr;

answered Feb 5, 2016 at 8:13

Daniel

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