#include<iostream>
using namespace std;
#define maxsize 50
double p(int n, double x) {
    struct stack    {        
    int no;    //保存n        
    double val;   //保存Pn（x）的值   
     }st[maxsize];
    int top = -1, i;
    double fv1 = 1, fv2 = 2 * x;
    for (i = n; i >= 2; i--){        
     top++;        
     st[top].no = i;   
      }
    while (top >= 0) {        
     st[top].val = 2 * x * fv2 - 2 * (st[top].no - 1) * fv1;       
     fv1 = fv2;      
     fv2 = st[top].val;   
            top--;   
             }    if (n == 0) 
             {       
              return fv1;  
                }   
               else {      
                 return fv2; }
                 }
double p2(int n, double x){    
if (n == 0){       
   return 1;   
   } else if (n == 1) {      
     return 2 * x;    
     } else if (n > 1) {      
        return 2 * x * p2(n - 1, x) - 2 * (n - 1) * p2(n - 2, x);    }
        }


int main() {    
int n = 5;    
double x = 5.00;    
double m = p(n, x);    
double i = p2(n, x);
cout << "i is : " << i << endl;    
cout << "m is : " << m << endl;
return 0;
    }