C++ 中是否有任何内置的阶乘函数？

Question

I have searched but I was not able to find this. Would anyone please tell me that if there is any built-in factorial function in c++ ?

Answer 1

Although there is no C function defined specifically for computing factorials, C math library lets you compute gamma function . Since Г(n) = (n-1)! for positive integers, using tgamma of i+1 yields i! .

If you use a user-defined factorial function, this would print identical numbers:

for (int i = 1 ; i != 10 ; i++) {
    printf("%lld %f\n", factorial(i), tgamma(i+1));
}

Demo.

1 1.000000
2 2.000000
6 6.000000
24 24.000000
120 120.000000
720 720.000000
5040 5040.000000
40320 40320.000000
362880 362880.000000

Note: Considering how easy it is to code up factorial function, using gamma to compute factorials is a lot like killing a fly with a sledgehammer.

Answer 2

不，标准库中没有这样的功能。

Answer 3

不，在标准 C++ 中，没有像 factorial 这样的函数，但是你可以在 boost 库中找到相同的功能： boost::math::factorial

Answer 4

STL doesn't provide function for Factorial but you can calculate in one line recursively:

int fact(int n){

     return (n==0) || (n==1) ? 1 : n* fact(n-1);
}

Answer 5

there is no function present for find factorial in c++ STL. you should write your own function for find factorial

Answer 6

Writing a slow version of factorial even with DP in C or C++ is easy. However, there is a much faster algorithm implemented in Python 3:

See https://hg.python.org/cpython/file/7937aa6b7e92/Modules/mathmodule.c#l1218

So, it would be good to add it to the STL imho.