WTF数组开三个大小都能过？

#include<bits/stdc++.h>
using namespace std;
int a[3];
int main(){
int n; cin >> n;
for(int i = 1; i <= n; i++){
cin >> a[i];
if(a[i] % 2 == 0) cout << a[i] << endl;
}
return 0;
}