Help me in solving LARGESECOND problem

My issue

can you tell what is required to remove compilation error

My code

#include <iostream>
#include <vector>
using namespace std;

int main() {
	// your code goes here
 
        
	    	int t;
	cin>>t;
	while(t--){
	    int n;
	    cin>>n;
	    int arr[n];
	    for(int i=0;i<n;i++){
	        cin>>arr[i];
	    }
	    sort(arr,arr+n,greater<int>());
	    for(int i=0;i<n-1;i++){
	        if(arr[i+1]==arr[i]){
	            continue;
	        }
	        cout<<arr[i]+arr[i+1]<<endl;
	        break;
	    }
	}
	return 0;
}

Learning course: Arrays using C++
Problem Link: CodeChef: Practical coding for everyone

@janhavipinjan7
use #include<bits/stdc++.h> header file.