calcul de suma_for

#include <iostream>
using namespace std;

int main()
{
   int n, i, suma=0, p;
   cout<<"Acesst program calculeaza suma de tipul:1^2-2^2+4^2-4^2+...+(-1)^(n+1)n^2"<<endl;
   cout<<"Introduceti n=";
   cin>>n;
   for(i=1; i<=n; i++)
   {  if(i%2==0)
         p=i*(-i);
        else
            p=i*i;

         suma=suma+p;
   }
   cout<<"Suma este:"<<suma;
    return 0;

}