code failing hidden test case.

my code is failing one hidden test case .please help!

Q)You will be provided with a number. Print the number of days in the month corresponding to that number.

Note: In case the input is February, print 28 days. If the Input is not in valid range print Error.

Input Description: The input is in the form of a number.

Output Description: Find the days in the month corresponding to the input number.

Print Error if the input is not in a valid range.

#include <iostream>

using namespace std;

int main() {

// your code goes here

int n;

cin>>n;

if(!(n==1 || n==2 || n==3 || n==4 || n==5 || n==6 || n==7 || n==8 || n==9 || n==10 || n==11 || n==12))

{

cout<<"Error";

return 0;

}

int a[n+1];

a[1]=31;

a[2]=28;

a[3]=31;

a[4]=30;

a[5]=31;

a[6]=30;

a[7]=31;

a[8]=31;

a[9]=30;

a[10]=31;

a[11]=30;

a[12]=31;

cout<<a[n];

return 0;

}