#include <iostream>

using namespace std;
bool primzahl(int zahl)
{
for(int j = 2; j*2<zahl;j++)
{
	if (zahl%j == 0)
	{
		return false;
	}
}
return true;
}

int main ()
{
long double a = 317584931803;
for(int i = 2; i <a/2;i++){
	if(a%i == 0){
		if(primzahl(i)){
			cout << i <<endl;
	}
}
}
}

Hier die Fehlermedung von g++ unter linux:

3.cpp:18: error: integer constant is too large for 'long' type
3.cpp: In function 'int main()':
3.cpp:20: error: invalid operands of types 'long double' and 'int' to binary 'operator%'