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

int main(int argc, char* argv[])
{
int N,Sum=0;
cout<<"Введите значение"<<endl;
cin>>N;
if(N>0 && N<=abs(1000))
{
 for(int i=0;i<=N;i++)
 {
    Sum+=i;
 }
 cout<<Sum;
}
if(N<0 && N<=abs(-1000))
{
  for(int j=0;j>=N;j--)
 {
    Sum+=j;
 }
cout<<Sum;
}    getch();
        return 0;
}

Edited by author 05.07.2013 20:36

Edited by author 05.07.2013 20:38

from the first glance: it's supposed to be 10000, not 1000