#include <stdio.h>
#include <stdlib.h>
#include <windows.h> 
int main()
{
	int i,j;
	int x = 0;
	int y = 5;
	
	int velocity_x = 1;
	int velocity_y = 1;
	int left = 0;
	int right = 20;
	int top = 0;
	int bottom = 10;
	
	while (1)
	{
		x = x + velocity_x;
		y = y + velocity_y;
		
		system("cls");   // 清屏函数
		// 输出小球前的空行
		for(i=0;i<x;i++)
			printf("\n");
		for (j=0;j<y;j++)
			printf(" ");
		printf("o");  // 输出小球o
		printf("\n"); 
		Sleep(50);  // 等待若干毫秒
		
		if ((x==top)||(x==bottom))
			velocity_x = -velocity_x;
		if ((y==left)||(y==right))
			velocity_y = -velocity_y;		
	}
	return 0;
}