How do you implement the factorial function in C++? [duplicate]
Possible Duplicates:
Calculating large factorials in C++ Howto compute the factorial of x
How do you implement the factorial function in C++? And by this I mean properly implement it using whatever argument checking and error handling logic is appropriate for a general purpose math library in C++.
Recursive:
unsigned int factorial(unsigned int n)
{
if (n == 0)
return 1;
return n * factorial(n - 1);
}
Iterative:
unsigned int iter_factorial(unsigned int n)
{
unsigned int ret = 1;
for(unsigned int i = 1; i <= n; ++i)
ret *= i;
return ret;
}
Compile time:
template <int N>
struct Factorial
{
enum { value = N * Factorial<N - 1>::value };
};
template <>
struct Factorial<0>
{
enum { value = 1 };
};
void foo()
{
int x = Factorial<4>::value; // == 24
int y = Factorial<0>::value; // == 1
}
Besides the obvious loops and recursions, modern C++ compilers support the gamma function as tgamma()
, closely related to factorial:
#include <iostream>
#include <cmath>
int main()
{
int n;
std::cin >> n;
std::cout << std::tgamma(n+1) << '\n';
}
test run: https://ideone.com/TiUQ3
You might want to take a look at boost/math/special_functions/factorials.hpp
if you have Boost installed. You can read about it at: Boost Factorial
精彩评论