Comparison of factorials using compile-time calculation vs runtime calculation.

factorial.cpp

#include <iostream>

// g++ -std=c++11 -pedantic -Wall -Werror -Wextra factorial.cpp -o factorial

template <typename type>
constexpr type constFactorial( type n ) {
    return (n > 1) ? n * constFactorial( n - 1 ) : n;
}

template <typename type>
inline type calcFactorial( type n ) {
    type r = ( n ) ? 1 : n = 0;
    
    while ( n )
        r *= n--;
    
    return r;
}

int main() {
    
    std::cout << "The factorial of " << 0 << " is " << constFactorial( 0 ) << std::endl;
    std::cout << "The factorial of " << 1 << " is " << constFactorial( 1 ) << std::endl;
    std::cout << "The factorial of " << 2 << " is " << constFactorial( 2 ) << std::endl;
    std::cout << "The factorial of " << 3 << " is " << constFactorial( 3 ) << std::endl;
    std::cout << "The factorial of " << 4 << " is " << constFactorial( 4 ) << std::endl;
    std::cout << "The factorial of " << 5 << " is " << constFactorial( 5 ) << std::endl;
    std::cout << "The factorial of " << 10 << " is " << constFactorial( 10 ) << std::endl;
    
    unsigned long long i = 0;
    unsigned long long f = 0;
    unsigned long long err = 0;
    
    do {
        i += 1;
        err = f;
        f = calcFactorial( i );
        
        if ( f < err )
            break;
        
        std::cout << "The factorial of " << i << " is " << f << std::endl;
        
    } while ( f );
    
    return 0;
}