Why this code is not working, time limit is exceeding?

#1

#include
#include<math.h>
using namespace std;
int main() {
int t;
cin>>t;
while(t–)
{
int n;
cin>>n;
int arr[1000002]={0};
arr[0]=1;
arr[1]=1;
for(long int i=2; i<=sqrt(1000001);i++)
{
if(!arr[i])
{
for(long int j=i*i; j<=1000001; j+=i)
{
arr[j]=1;
}
}
}
for(long int i=2; i<=1000001&&n>0; i++)
{
if((n==1)&&(arr[i]==0))
{
cout<<i<<endl;
break;
n–;
}
else if(arr[i]==0)
n–;
}
}
return 0;
}

#2

You need to use prime seive optimisation in your code as given in the online video lecture in number theory section as,
p[0]=p[1]=0;
for(long long int i=3;i<=N;i=i+2)
{
p[i]=1;
}
for(long long int i=3;i<=N;i=i+2)
{
if(p[i])
{
for(long long int j=ii;j<=N;j=j+2i)
{
p[j]=0;
}
}
}