那位大佬看看这是怎么回事啊？呜呜呜呜呜

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


int sum = 1;
int main(){
	vector<int> v;
	int n;
	cin >> n;
	int a[n];
	for(int i = 0;i<n;i++){
		cin >> a[i];
	}
	for(int i = 0 ;i<n;i++){
		if(a[i+1] > a[i])
		sum++;
		else{
			v.push_back(sum);
			sum = 1;
		}
	}
	vector<int>::iterator itmax = max_element(v.begin(),v.end());
	cout << *itmax;
	return 0 ;
}
  
  报错是11测试点错误
  输入：6
  1 2 1 2 3 4 
  输出：4