判断素数

#include <iostream>
#include <cmath>
using namespace std;
int f(int n);
int main()
{
 int n;
 int k=0;
 while(cin>>n)
  if(f(n))
   cout<<"Case "<<++k<<": "<<"Number "<<n<<" is not prime."<<endl;
  else
   cout<<"Case "<<++k<<": "<<"Number "<<n<<" is prime."<<endl;

 return 0;
}
int f(int n)
{
 int i,m;
 m=(int)sqrt(double(n));
 for(i=2;i<=m;i++)
  if(n%i==0) break;
 if(i<=m)
  return 1;
 else
  return 0;
}