谁用谁知道。。

#include<bits/stdc++.h>
using namespace std;
const int mx = 20;
const double period = 10.0;

int main()
{
	for (int i = 0;; i = (i + 1) % (2 * mx))
	{
		double starttime = clock();
		while (clock() - starttime < period);
		for (int j = 0; j < mx; ++j)
			putchar('\b');
		int j;
		for (j = 0; j < (i <= mx ? i : (2 * mx) - i); ++j)
			putchar('.');
		for (; j < mx; ++j)
			putchar(' ');
	}
	return 0;
}