Problema risolto scusate. Ho scritto così:
#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
cout << "a number in decimal: " << dec << 15 <<endl;
cout << "in octal:" << oct << 15 << endl;
cout << "in hex:" << hex << 15 << endl;
cout << "a floating - point number : " << 3.14159 << endl;
cout << "non printing char (escape): " << char(27) << endl;
system("PAUSE");
return EXIT_SUCCESS;
}