因子不适用于所有值 [英] Factorial does not work for all values

问题描述

大家好，我编辑了我的帖子，因为我有另一个问题，我的代码。我有一个问题的阶乘函数昨天，但我设法解决它感谢你的答案，这是一个可笑的错误。
现在的问题是，对于一些高于15的值，最后的结果（不是个别数字的阶乘）总是0或-1为更小的值它工作正常。有人告诉我什么错误此代码：

  #include< iostream> 
＃include< time.h> 
 
 using namespace std; 
 
 
 
 int factorial（int a）{
 if（a == 1）
 return 1; 
 else if（a == 0）
 return 1; 
 else 
 return factorial（a-1）* a; 
 
} 
 
 int main（）{
 std :: cout.setf（std :: ios_base :: fixed，std :: ios_base :: floatfield）; 
 std :: cout.precision（5）; 
 int n，k; 
 int x，y，z，w，v; 
 
 
 cout<<give n：; 
 cin>> n; 
 
 
 cout<<give k：; 
 cin>> k; 
 
 clock_t t; 
 
 t = clock（）; 
 
 
 
 if（n> = k& k> 1）{
 
 x = factorial（n-1） 
 y = factorial（k-1）; 
 z = factorial（n-1-k）; 
 w = factorial（n-k）; 
 v = factorial（k）; 
 
 
 cout<<结果是<<（x /（v * z））+（x /（y * w））< 
} 
 else if（n == 0 || n == k）
 cout<<Result is 1<< endl; 
 else 
 cout<<Result is 0<< endl; 
 
 
 t = clock（） -  t; 
 cout<<需要<<<<clicks（<<（（float）t）/ CLOCKS_PER_SEC<<seconds）< 
 
 
 
 return 0; 
} 
  

解决方案

>

如果 int 在您的系统上是32位，则它可以表示的最大值为 2147483647 。如果您使用64位整数类型，例如，那么

$ b <

浮点会给你更多的范围，但精度的损失。

/ p>

如果你真的需要计算大的阶乘，你需要使用一些多精度库，例如 GMP ，或使用内置任意精度整数运算的语言（C不是）。

Hi everyone I edited my post because I have another problem with my code.I had a problem with the factorial function yesterday but I managed to solve it thanks to your answers , it was a ridiculous mistake. The problem now is that for some values that are higher than 15, the final results(not the factorials of individual numbers) are always 0 or -1 for the lesser values it works fine.Can someone tell me whats wrong with this code :

    #include <iostream>
    #include<time.h>

    using namespace std;



    int factorial(int a){
    if(a==1)
      return 1;
    else if(a==0)
      return 1;
    else 
      return factorial(a-1)*a;

    }

    int main(){
    std::cout.setf(std::ios_base::fixed, std::ios_base::floatfield);
    std::cout.precision(5);
    int n,k;
    int x,y,z,w,v; 


    cout<<"give n : ";
    cin>>n;


     cout<<"give k : ";
     cin>>k;

     clock_t t;

        t = clock();



      if(n>=k&&k>1){

       x=factorial(n-1);
       y=factorial(k-1);
       z=factorial(n-1-k);
       w=factorial(n-k);
       v=factorial(k);


         cout<<"Result is "<<(x/(v*z))+(x/(y*w))<<endl;
       }
       else if (n==0||n==k)
         cout<<"Result is  1"<<endl;
       else
         cout<<"Result is  0"<<endl;


       t = clock() - t;
       cout<<"It took "<<t<<" clicks  ("<<((float)t)/CLOCKS_PER_SEC<<" seconds )"<<endl;    



       return 0;
       }

解决方案

Integer overflow.

If int is 32 bits on your system, the largest value it can represent is 2147483647. 13 factorial is 6227020800.

If you use a 64-bit integer type such a long long, you can go up to 20 factorial.

Floating-point will give you more range, but with a loss of precision.

If you really need to compute large factorials, you'll need to use some multi-precision library like GMP, or use a language that has built-in arbitrary-precision integer arithmetic (C doesn't).

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