#include <iostream>
#include <vector>
 
void modify(std::vector<int> &v);
 
int main () {
  std::vector<int> foo {16, 2, 77, 40, 12071};
 
  modify(foo);
 
  for(auto i : foo) std::cout << i << " ";
  std::cout << std::endl;
 
  return 0;
}
 
void modify(std::vector<int> &bar) {
  // baz points to (for example) memory location 4567
  std::vector<int> baz(bar.size());
 
  // this loop can't modify my data in-place,
  // so it uses baz temporarily
  for(int i(0), sz(bar.size()); i < sz; ++i){
    int j;
    if(i == 0) j = 4;
    else j = i - 1;
    baz[i] = bar[i] + bar[j];
  }
  bar.swap(baz);
}

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