From: Panagiotis Atmatzidis <atma@...>
Date: 2010-01-04T01:53:44+09:00
Subject: Re: Few clarifications on recursion

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Hello
On 03 =CE=99=CE=B1=CE=BD 2010, at 6:46 =CE=BC.=CE=BC., Josh Cheek wrote:

>>=20
>> Although it introduces many interesting concepts to me (i. e. I did =
not
>> knew that after the "if" statement a single _1_ with no quotes could =
be
>> used) I fail to see how the num changes value. The way I read the =
code here:
>>=20
>>=20
> In Ruby, the last line of a function is returned. In this case, the =
last
> line is the if statement. The if statement evaluates to the last line =
of
> code inside of it. This means that if the number is less than or equal =
to 1,
> the last line of the if statement will be 1, so that is what the if
> statement will evaluate to, and thus that is what the function will =
return.

Okay returns the last statement, but is it a number or a string?

>=20
>=20
>> num * factorial(num-1)
>>=20
>> is 30*29 for "puts factorial(30)" not 30*29*28... which is how it =
works.
>> I've tested the code works fine.
>>=20
>>=20
> This is the recursive portion, it is not 30*29, it is =
30*factorial(29), and
> factorial(29) is 29*factorial(28) and factorial(28) is =
28*factorial(27)
> etcetera until you get to 1, and factorial(1) is just 1, because it is =
less
> than or equal to 1.
>=20
> If you expand these calls out, you get 30*( 28*( 27*( ... *(1) ) ) )
>=20
>=20
> If you are still confused by this, try going the other way. Start with =
1,
> and go up. If factorial(1) returns 1, what will factorial(2) return =
(go
> through the code)? And then what will factorial(3) return? And so on.


Yes you are right. Now I get it. Thank you for pointing this out for =
nicely!

So this is the whole point of recursion to run the program (backwards in =
this case) until the even that will stop the recursion happens.

Thanks to all & regards

Panagiotis (atmosx) Atmatzidis

email:	atma@convalesco.org
URL:	http://www.convalesco.org
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--
The wise man said: "Never argue with an idiot. They bring you down to =
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