C++ pre-increment vs post-increment

main.cpp

#include <vector>
#include <chrono>
#include <iostream>

using namespace std;

int main() {
  int n = 1000000;
  int value = 42;
  vector<int> vec(n, value);
  int sum = 0;
  
  auto start = chrono::steady_clock::now();
  for(auto el = vec.begin(); el != vec.end(); el++) {
    sum += *el;
  }
  auto end = chrono::steady_clock::now();
  
  cout << "Post-increment : " 
	  << chrono::duration_cast<chrono::microseconds>(end - start).count()
		<< " µs" << endl;
  
  sum = 0;
  
  start = chrono::steady_clock::now();
  for(auto el = vec.begin(); el != vec.end(); ++el) {
    sum += *el;
  }
  end = chrono::steady_clock::now();
  
  cout << "Pre-increment : " 
	  << chrono::duration_cast<chrono::microseconds>(end - start).count()
		<< " µs" << endl;
  
  return 0;
}