编写程序使一只鸟的图形飞过屏幕（来回两次）。飞鸟的动作可由小写字母 v（ASCII 码 76H）变为破折号（ASCII 码 0C4H）来模仿，这两个字符先后交替在两列上显示。鸟的开始位置是0 列20 行，每个字符显示1/10秒，然后消失。-Program the movement of a bird flying graphics screen (twice) back and forth. The birds Actions by lowercase letters v (ASCII code 76H) becomes a dash (ASCII code 0C4H) to mimic these two characters are successively displayed alternately on two columns. The birds start position 0 20 rows, each character is 1/10 second and then disappears.