quicksort algorithm in C++

qsort.cpp

#include <iostream>
#include <math.h>
#include <vector>

using namespace std;

void qsort(vector<int>& v){
  if (v.size() > 1){
    int pivot = floor(v.size()/2);
    vector<int> left;
    vector<int> right;
    right.push_back(v[pivot]);
    for (int i=0; i<v.size(); i++){
      if(i != pivot){
        if(v[i]<v[pivot]){
          left.push_back(v[i]);
        }
        else{
          right.push_back(v[i]);
        }
      }
    }
    qsort(left);
    qsort(right);
    //merge left and right into a single vector
    vector<int> sorted;
    sorted.reserve(left.size() + right.size());
    sorted.insert(sorted.end(), left.begin(), left.end());
    sorted.insert(sorted.end(), right.begin(), right.end());
    //
    v.swap(sorted);
  }
}

int main(){
  vector<int> v;
  for(int i=0; i<20; i++){
    v.push_back(round(rand()));
  }

  qsort(v);
  for (int i=0; i<v.size();i++){
    cout<<v[i]<<'\n';
  }
}