c++ - 你如何在 C++ 中实现阶乘函数？

Question

Possible Duplicates:
Calculating large factorials in C++
Howto compute the factorial of x

如何在 C++ 中实现阶乘函数？我的意思是使用适用于 C++ 中的通用数学库的任何参数检查和错误处理逻辑来正确实现它。

Answer 1

递归:

unsigned int factorial(unsigned int n) 
{
    if (n == 0)
       return 1;
    return n * factorial(n - 1);
}

迭代:

unsigned int iter_factorial(unsigned int n)
{
    unsigned int ret = 1;
    for(unsigned int i = 1; i <= n; ++i)
        ret *= i;
    return ret;
}

编译时间:

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
}