程序代码：

#include <stdio.h>
#include <conio.h>
#include <time.h>

#define N    (double)1E9

void main(void)
{
    clock_t Start_Time, End_Time;

    Start_Time = clock();
    printf_s("Sum = %.0f\n", N * (N + 1) / 2);
    End_Time = clock();

    printf_s("Run time is %6.4fs\n", (double)(End_Time - Start_Time) / CLOCKS_PER_SEC);

    _getwch();
}