#include <iostream>
#include <math.h>
#include <windows.h>
using namespace std;
int main()
{
    short int i;
    float a[20];
    for(i=0;i<20;i++){
       cout<<"a["<<i+1<<"]=";
       cin>>a[i];
    }
    if(a[20]>0){
       float D;
       D=1;
       for(i=0;i<20;i++){
           if(a[i]<0){                  
              D*=a[i];
           }
       }
       cout<<"D="<<D<<endl;
    } else {
       int P;
       P=1;
       for(i=0;i<20;i++){
       if(i%2==0)
           {
           P*=a[i];
           }
       }
       cout<<"P="<<P;
   }
    system ("pause");
    return 0;
}

#include <iostream>
#include <conio.h>
using namespace std;

int main()
{
    const short int size = 20;
    double x[size];

    for (int i = 0; i < size; ++i)
        cin >> x[i];

    double product = 1;

    if (x[19] > 0)    {
        for (int i = 0; i < size; ++i)
        {
            if (x[i] < 0)
                product *= x[i];
        }

    }
    else    {
        for (int i = 1; i < size; i += 2)
            product *= x[i];
    }

    cout << "\n" << "Result = " << product << endl;
    _getch();
    return 0;
}