LOGO 海龟作画系列三递归画一个国际象棋棋盘 Logo Turtle Graphics - Series 3 - Recursively drawing a chess board

justyy (82)in #cn • 7 years ago (edited)

本系列：

Logo Tutorial Series：

今天我们要来讲一讲递归。递归就是函数自己调用自己，我们可以定义一个过程，然后这只海龟不停的画，结束的时候再调用自身再继续画。再次调用的时候参数变化了，至到参数满足一定的条件则停止。

A recursion is a function calling itself. In Logo, we can define a procedure, asking the turtle to draw something, then ask the turtle to repeat itself but with slightly different parameters, until a set of conditions are met.

比如下面定义的这个过程可以用来画一个实现的正方形。
For example, the following procedure can be used to draw a filled rectangle.

TO FK :B
  IF :B>15 [STOP]  ; 如果边长大于15就停止
  REPEAT 4 [FD :B RT 90] ; Draw a square with side B 画一个长度为B的正方形
  FK :B+1  ;  Draw a square with side B+1 递归调用自己画一个长度为B+1的正方形
END

然后我们可以通过调用 FK 15 来画一个空心的正方形，这样的话，通过不停的画空心实心(不断交错)则可以构成一个棋盘：
The FK 15 draws a empty square. By such, we can draw the interleaving squares.

TO QP :Y
  IF :Y>4 [STOP]   
  REPEAT 4 [FK 15 FD 15 FK 1 FD 15] 
  RT 90 FD 30 RT 90
  REPEAT 4 [FK 15 FD 15 FK 1 FD 15]
  RT 180
  QP :Y+1
END

您可以使用我写的这个PHP-LOGO解释器来验证这段LOGO代码。
You could use this PHP-LOGO Interpreter to verify the LOGO program as stated above.

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原创 https://Steemit.com 首发。感谢阅读，如有可能，欢迎Follow, Upvote, Reply, ReSteem (repost) @justyy 激励我创作更多更好的内容。

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