I need help using recursion in OOP: : A level 1 tree is a line. A level 2 tree is a line and two level 1 trees (it looks like: Y). A level 3 tree is a line and two level 2 trees. A level 4 tree is a line and two level 3 trees.

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Kyle Reagan
Kyle Reagan 2016-10-14
评论： Steven Lord 2016-10-17
I have a class set up with functions to drive forward and make turns. I just don't know how to make this work in a loop. The following is what the program should do for a n-level tree. If n is 0, do nothing. Otherwise, drive forward d, turn left a degrees, draw a level n-1 tree, turn right 2a degrees, draw a level n-1 tree, turn left a degrees, and drive backward d
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Kyle Reagan
Kyle Reagan 2016-10-14
t = Turtle(); a = 40; b = 4; while n > 0
t = t.fd(b);
t = t.lt(a);
t = t.fd(b);
t = t.bk(b);
t = t.rt(2*a);
t = t.fd(b);
t = t.bk(b);
t = t.lt(a);
t = t.bk(b);
end
This is what I have so far.

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回答（1 个）

Steven Lord
Steven Lord 2016-10-14
Ah, LOGO and turtle graphics. That takes me back ... longer ago than I'd care to admit.
Is the code you posted in a function named tree or something similar? If it is, what input arguments does the function accept? If it is not in a function, you should create a function named tree. For this to be a recursive program, the tree function will have to call itself.
I would put each clause (a section ending in a period or a comma) in your instructions on how to draw the tree on a separate line of your file as a comment. Then after each of those comment lines, write a single command that does what the comment line says to do.
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Kyle Reagan
Kyle Reagan 2016-10-17
Now I have it so that my input is n and my output is y.
obj = Turtle(); function [y] = tree(obj,n) % Creates tree to the order n t = Turtle(); a = 60; % angle in degrees d = 4; % distance turtle travels
% If n is 0, if n <= 0 % do nothing. t = t.fd(0); % Otherwise, else % drive forward d, t = t.fd(d); % turn left a degrees, t = t.lt(a); % draw a level n-1 tree, y = tree(n-1) % turn right 2a degrees, t = t.rt(2*a); % draw a level n-1 tree, y = tree(n-1) % turn left a degrees, t = t.lt(a); % and drive backward d t = t.bk(d); end end
Steven Lord
Steven Lord 2016-10-17
Almost. You've defined tree to have two inputs, obj and n. You're calling it in your recursive step with one input, just n-1. You should call it with two inputs, obj and n-1. Otherwise at the recursion step when you execute "if n <=0" the variable n won't exist and you'll receive an error.

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