Essential C++ : Calculating Factorials https://www.programming-books.io/essential/cpp/calculating-factorials-317f96c51a284c9ab5e0bf64625f5d70 (made with https://codeeval.dev)

main.cc

#include <iostream>

template<unsigned int n>
struct factorial
{
    enum
    {
        value = n * factorial<n - 1>::value
    };
};

template<>
struct factorial<0>
{
    enum { value = 1 };
};

int main()
{
    std::cout << factorial<7>::value << std::endl;    // prints "5040"
}