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++.
Algorithm of Factorial Program in C Read the integer and assign it to a variable. From the value of the integer up to 1, multiply each digit and update the final value. The final value at the end of all the multiplication till 1 is the factorial.
Although there is no C function defined specifically for computing factorials, C math library lets you compute gamma function.
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
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