dynamically allocated arrays with user input c++ - c++

Question

I want to have a mini function that allows the user to type a group of numbers, and each of them will be dynamically allocated into an array. For example:
int main()
{
int* x = NULL;
int n, numbers;
std::cin >> n;
x = new int[n]
for (int i=0;i<n;i++){
std::cin >> numbers;
x[i] = numbers;
}
delete [] x;
So when the user types in
3
The user will be able to type in 3 numbers following that
3 1 2 3
I am trying to store the values 1, 2, 3 into an array so it will look like
[1, 2, 3]
but right now it's storing as
[123]
Anyway i can fix this? I'm new to C++ programming so I feel like there's an easy solution to this but i'm not sure how.. thank you!

Answer 1

You could store each element of the array directly into x[i]. Not sure what numbers is used for (I've assigned numbers from x[i]).
x is the array that is to be deleted. And there is a missing ; at x = new int[x] - is that a typo?
int main()
{
int* x = NULL;
int n, numbers;
std::cin >> n;
x = new int[n];
for (int i=0;i<n;i++){
std::cin >> x[i];
numbers = x[i];
}
delete [] x;

Answer 2

You can use a vector instead:
#include <iostream>
#include <vector>
using namespace std;
int main()
{
int n;
cin >> n;
vector<int> v;
for (int i = 0; i < n; ++i)
{
int val;
cin >> val;
v.push_back(val);
}
}
C++'s vector takes care of memory allocation for you. You could then simply traverse it and print its contents.
cout << "[";
for (int i = 0; i < v.size(); ++i)
{
if (i != 0)
cout << ",";
cout << v[i];
}
cout << "]";

Answer 3

Example 1
int main()
{
int* x = NULL;
int n, numbers;
std::cin >> n;
x = new int[n]; // need a semi-colon here
for (int i=0;i<n;i++)
{
std::cin >> numbers;
x[i] = numbers;
}
for (int j = 0; j < n; ++j)
{
std::cout << "x[" << j << "] = " << x[j] << std::endl;
}
delete [] x; // you mean x, not a
return 0;
}
Once you fix (what I assume are just typos), what you have works fine. However, unless this is for an assignment, you should consider using std::vector instead of raw dynamic memory allocation. Doing so would reduce your code to about 4 lines.
int main()
{
std::vector<int> myvector;
std::copy(std::istream_iterator<int>(std::cin), std::istream_iterator<int>(), std::back_inserter(myvector));
std::copy(myvector.begin(), myvector.end(), std::ostream_iterator<int>(std::cout, "\n"));
return 0;
}
or, in C++11
int main()
{
std::vector<int> myvector{std::istream_iterator<int>(std::cin), std::istream_iterator<int>()};
std::copy(myvector.begin(), myvector.end(), std::ostream_iterator<int>(std::cout, "\n"));
return 0;
}

Answer 4

Why not just create the array dynamically? This way, the user won't have to type in the number of elements in advance:
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> vec;
int x;
while (cin >> x)
vec.push_back(x);
for (int y: vec)
cout << y << ' ';
cout << '\n';
}
The cout statements are just to illustrate that everything worked.