[Tutor] finding factorials - hmm..., gcd

[Gregor Lingl]

Payal Rathod schrieb:

>On Tue, Jul 01, 2003 at 11:15:01AM +0100, glingl wrote:
>  
>
>>Your code is ok and gives the right result!
>>e.g change:  x, y = 25, 15 and you will get:
>>    
>>
>
>Are you sure? I mean I don't get what a common factor means? Can you
>tell?
>
>  
>
>># (1) normally it's not considered good practice to pu
>>#     print-statements in a function which aims at calculating
>>#     a numerical rsult. - 
>>    
>>
>
>
>Why??? I mean it is good for troubleshooting/debugging.
>
Yes! (But didn't I say that?)

>
>  
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>># (2) here you use an uncoditional return - so the body of
>>#     the while-loop will be exited after the first run. 
>>    
>>
>
>I don't get this. You mean to say that once I type return euclid(a,b),
>the while loop stops? 
>
Not only the while-loop stops but the execution of the program leaves
the (code of the) function  and continues with finishing the statement, 
which contains
the function call  - in your case an assignment, which assigns the returned
value to the variable result.

>Why? 
>
This is the purpose the return-statement is intended for

>Also, if it does not get executed 
>
I didn't say, that the body of the while loop doesn't get executed. I
said that it *invariably* is executed *only_once*, which is not was
a loop is normally meant for.

>how am I
>getting right answers as you say?
>  
>
Because it does the same as the code of the recursive correction
(that is the second one) in my posting.

>  
>
>>#     Consequently it will never work as a loop and you could
>>#     (a)  use an if instead of while or
>>    
>>
>
>Can you point a small example in *this* context using an if statement?
>

I think, I gave you two "small" examples exactly in *your_context*, 
namely two different possible
modifications of your code -
(a) the first one resulting in a euclid-function using a while loop (BUT 
NO RECURSION) and
(b) the second one using recursion (BUT NO WHILE-LOOP)

>>#     (b)  drop the return and recursive call of euclid - 
>>#          recursion also accomplishes some sort of iteration
>>#          and should/need/(must?) not be done in addition 
>>#          to the while-iteration  
>>    
>>
>
>I didn't get your meaning on this too, please.
>  
>
A recursive functions calls itself (again, several times, until the 
stop-condition is reached), so
its code is executed repeatedly.

>># (3) here you can leave out the three statements
>>#
>>#               c = a
>>#               a = b
>>#               b = c % a
>>#
>># if think carefully about which values are to be
>># inserted as arguments in the recursive function
>># call.
>># What are the values of a and b respectively after
>># execution of these 3 statements. (Remember: ist is
>># perfectly right to insert arithmetic expressions like
>># a / b, a+b etc as arguments - in which case they
>># will be computed (evaluated( before the results are 
>># "bound" to the parameters.)
>>    
>>
I fear, my crude English is responsible, that you don't understand what I
mean. Although just this maybe really hard to grasp. I wont't give an
explanation, more gifted people exist on this list. Just try the following
code and think about it:

print "WHAT'S GOING ON?"
x =4
y=10
z = 0
print "x =",x,"y =",y,"z =",z

def look(a,b):
    print "x =",x,"y =",y,"z =",z,"a =",a,"b =",b
    a=2*a
    b=2*b
    c=a*b
    print "x =",x,"y =",y,"z =",z,"a =",a,"b =",b,"c =",c
    return c
    c = c*c       # ;-)
    print "x =",x,"y =",y,"z =",z,"a =",a,"b =",b,"c =",c   # or: :-( ?

print "x =",x,"y =",y,"z =",z
z = look(x,y)     # this will execute 2 (!) print-statements
# you won't be able to print a,b,c here
print "x =",x,"y =",y,"z =",z

Regards, Gregor

>Ahh! Sorry again, I didn't get you. I don't understand much programmers
>jargon. The whole paragraph looks greek to me.
>
>  
>
>>P.S.: Maybe http://www.ibiblio.org/obp/thinkCSpy/ ,
>>especially chapters 4 to 6,
>>contains material, which could be helpful for you. 
>>    
>>
>
>I had read them 2 days back. Maybe I should read them again.
>
>
>Thanks a lot for the time and patience.
>With warm regards,
>-Payal
>
>  
>