Sorting in o(n)time. please see my code

#1

#include
using namespace std;

int main() {

int n;
cin>>n; //size of array

int a[3],i,p;

for(i=0;i<n;i++)
 { 
    cin>>p;
    a[p]++;
 }

i=0;
for(i=0;i<3;i++)
{
   while(a[i]!=0)
    {
		cout<<i<<endl;
		a[i]--;     
     }
}

return 0;

}

#2

firstly u have to take size of a upto which u can enter the value
like the value can be upto 10^18 so u cannot declare that much size in array

2nd u have to check array for the last value u have enter and inside this there is a while loop which is printing all occurunce of a value

so time complexity is not o(n)
hope this help:)