primes.cpp

//
//  Erwin Unruh implemented this first, prime numbers were printed out as warnings
//

#include <iostream>
 
template <int p, int i>
class is_prime {
public:
  enum { prim = (p==2) || ((p%i) && is_prime<( i>2 ? p : 0),i-1>::prim) }; 
}; 
 
template<>
class is_prime<0,0> {
public:
	enum {prim=1};
}; 
 
template<>
class is_prime<0,1> {
public:
	enum {prim=1};
}; 
 
template <int i>
class Prime_print {      // primary template for loop to print prime numbers
public:
	Prime_print<i-1> a; 
	enum { prim = is_prime<i,i-1>::prim
	}; 
	void f() {
		if (prim)
		{
			std::cout << "prime number:" << i << std::endl;
		}
		a.f();
	} 
}; 
 
template<>
class Prime_print<1> {   // full specialization to end the loop
public:
	enum {prim=0}; 
	void f() {
	}; 
}; 
 
 
int main()
{
   Prime_print<100> a; 
   a.f(); 
}