Duplicate Elements in an array

//by using nested loops finding if there are nested elements so creating a vector and pushing into the vector.
//we can create a map and and if the frequency is greater than 1 we can push into that vector
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int n;
    vector<int>result;
    cin>>n;
    int a[n];
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
    }
    for(int i=0;i<n;i++)
    {
        for(int j=i+1;j<n;j++)
        {
            if(a[i]==a[j])
            {
                result.push_back(a[i]);
            }
        }
    }
    for(int i=0;i<result.size();i++)
    {
        cout<<result[i];
    }
    return 0;

}