Tính S(n) = 1-2+3-4+5+...+((-1)^(n+1))*n (n>0)

// Tinh P(n) = 1-2+3-4+5+...+((-1)^(n+1))*n (n>0)

 #include <iostream>

using namespace std;

 int Nhap()

{

   int x;

   do

   {

             cin >> x;

             if (x < 0)

                       cout << "Nhap sai, yeu cau nhap lai!";

   } while (x < 0);

   return x;

}

 long Tinh(int n)

{

   long p = 0;

long tmp = 1;

   for (int i = 1; i <= n; i++)

{

             p += tmp*i;

             tmp *= -1;

}

   return p;

}

int main()

{  int n;

   cout << "Nhap so nguyen n: ";

   n = Nhap();

   cout << "Ket qua la: "<< Tinh(n) << endl;

   return 0;