#include <iostream>
#include <vector>
using namespace std;
void f(unsigned N)
{
const unsigned stack_array_size=10;
char stack_array[stack_array_size];
vector<char> heap_array;
char *arr=stack_array;
if(N>stack_array_size)
{
heap_array.resize(N);
arr=&heap_array[0];
}
// use arr here
}
int main()
{
f(20);
}
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