// Program: sum_n.cpp
// Compute the sum of the first n natural numbers.
#include
int main()
{
// input
std::cout << "Compute the sum 1+...+n for n =? ";
unsigned int n;
std::cin >> n;
// computation of sum_{i=1}^n i
unsigned int s = 0;
for (unsigned int i = 1; i <= n; ++i) s += i;
// output
std::cout << "1+...+" << n << " = " << s << ".\n";
return 0;
}