Example
// Example of raw dynamic size array. It's generally better to use std::vector.
#include <algorithm> // std::sort
#include <iostream>
using namespace std;
auto int_from( istream& in ) -> int { int x; in >> x; return x; }
auto main()
-> int
{
cout << "Sorting n integers provided by you.\n";
cout << "n? ";
int const n = int_from( cin );
int* a = new int[n]; // ← Allocation of array of n items.
for( int i = 1; i <= n; ++i )
{
cout << "The #" << i << " number, please: ";
a[i-1] = int_from( cin );
}
sort( a, a + n );
for( int i = 0; i < n; ++i ) { cout << a[i] << ' '; }
cout << '\n';
delete[] a;
}
A program that declares an array T a[n]; where n is determined a run-time, can compile with certain compilers that support C99 variadic length arrays (VLAs) as a language extension. But VLAs are not supported by standard C++. This example shows how to manually allocate a dynamic size array via a new[]-expression,
int* a = new int[n]; // ← Allocation of array of n items.
… then use it, and finally deallocate it via a delete[]-expression:
delete[] a;
The array allocated here has indeterminate values, but it can be zero-initialized by just adding an empty parenthesis (), like this: new int[n](). More generally, for arbitrary item type, this performs a value-initialization.
As part of a function down in a call hierarchy this code would not be exception safe, since an exception before the delete[] expression (and after the new[]) would cause a memory leak. One way to address that issue is to automate the cleanup via e.g. a std::unique_ptr smart pointer. But a generally better way to address it is to just use a std::vector: that's what std::vector is there for.
