Write a recursive function in C or C++ to calculate the Nth number in the Fibonacci sequence

#include <iostream>
using std::cout;
using std::endl;
using std::cin;
 
unsigned long long f(int);
 
int main() {
    cout << "F(n), n = ";
    int n;
    cin >> n;
    if(n > 0)
        cout << "F(n) = " << f(n) << endl;
    else
        cout << "American?" << endl;
 
    system("pause");
    return 0;
}
 
unsigned long long f(int n) {
    if(n == 1)
        return 0ULL;
    else if(n == 2)
        return 1ULL;
    else
        return f(n - 1) + f(n-2);
}

#include <type_traits>
#include <iostream>
 
template <std::size_t N>
struct Fib : std::integral_constant<unsigned long long, Fib<N-1>::value + Fib<N-2>::value>
{};
 
template <>
struct Fib<1> : std::integral_constant<unsigned long long, 1>
{};
 
template <>
struct Fib<0> : std::integral_constant<unsigned long long, 1>
{};
 
int main()
{
   std::cout << Fib<0>() << "\n";
   std::cout << Fib<1>() << "\n";
   std::cout << Fib<2>() << "\n";
   std::cout << Fib<3>() << "\n";
   std::cout << Fib<4>() << "\n";
   std::cout << Fib<5>() << "\n";
   std::cout << Fib<6>() << "\n";
   std::cout << Fib<7>() << "\n";
   std::cout << Fib<8>() << "\n";
   std::cout << Fib<9>() << "\n";
}

Fib<N-1>::value + Fib<N-2>::value

constexpr uint64_t fib(uint32_t n)
{
    if (n == 0) return 0;
    if (n == 1) return 1;
    return fib(n - 1) + fib(n - 2);
}