Asp Forum - C(++) For Loop Equivalents

studlee2@gmail.com

3/20/2007 12:28:00 AM

What is the most efficient way in Ruby to create a conditional loop in
Ruby that looks like this in C(++):

for(int i=0; i*j/2<maxNum; i++)
{
//cool method stuff
}

I was looking at the .upto() method but it doesn't like the comparison
operator :-/

Thanks!

5 Answers

Austin Ziegler

3/20/2007 12:36:00 AM

On 3/19/07, studlee2 <studlee2@gmail.com> wrote:
> What is the most efficient way in Ruby to create a conditional loop in
> Ruby that looks like this in C(++):
>
> for(int i=0; i*j/2<maxNum; i++)
> {
> //cool method stuff
> }
>
>
> I was looking at the .upto() method but it doesn't like the comparison
> operator :-/

Wouldn't it be better to figure out what you're trying to do than look
for a general construct?

>> max = 200
=> 200
>> j = 35
=> 35
>> i = 0
=> 0
>> 0.upto(max) { |i| break if (i * j / 2) >= max }
=> nil
>> i
=> 12

That will do the job.

-austin
--
Austin Ziegler * halostatue@gmail.com * http://www.halo...
* austin@halostatue.ca * http://www.halo...feed/
* austin@zieglers.ca

Raj Sahae

3/20/2007 5:05:00 AM

studlee2 wrote:
> What is the most efficient way in Ruby to create a conditional loop in
> Ruby that looks like this in C(++):
>
> for(int i=0; i*j/2<maxNum; i++)
> {
> //cool method stuff
> }
>
>
> I was looking at the .upto() method but it doesn't like the comparison
> operator :-/
>
> Thanks
Why not just do:
((maxNum*2)/(i*j)).times do |n|
#cool method stuff
end

Michael W. Ryder

3/20/2007 5:25:00 AM

Raj Sahae wrote:
> studlee2 wrote:
>> What is the most efficient way in Ruby to create a conditional loop in
>> Ruby that looks like this in C(++):
>>
>> for(int i=0; i*j/2<maxNum; i++)
>> {
>> //cool method stuff
>> }
>>
>>
>> I was looking at the .upto() method but it doesn't like the comparison
>> operator :-/
>>
>> Thanks
> Why not just do:
> ((maxNum*2)/(i*j)).times do |n|
> #cool method stuff
> end
>

He would need to initialize i before your code as it could be any value,
not just 0. By the same token the increment could be any number, not
just 1.
A further problem with your method is that the loop is executed until
i*j/2 is greater than maxNum. As you don't know if the loop somehow
modifies the value of j you can not optimize it out. A simple example
would be where the program reads some numbers from a file and adds them
to j. i is incremented by one each time a number is read. You want the
program to exit when i*j/2 is larger than maxNum.

Peña, Botp

3/20/2007 10:25:00 AM

From: Michael W. Ryder [mailto:_mwryder@worldnet.att.net] :

# He would need to initialize i before your code as it could be
# any value,
# not just 0. By the same token the increment could be any number, not
# just 1.

fwiw, this is a simple example (intended for nubies only).

C:\family\ruby>cat -n test.rb
1 #---------------------------
2 #emulate c++ for (the better)
3 #for(int i=0; i*j/2<maxNum; i++)
4 # {
5 # //cool method stuff
6 # }
7 #---------------------------
8
9 # using normal while loop
10 puts "using while..."
11 j=20
12 i=0
13 maxnum=100
14 while i*j/2 < maxnum do
15 puts i
16 i+=1
17 end
18
19 # let's make our own for() and call it for_simple :)
20 # note, there's no condition here
21 # we're leaving it up to yield/blocks since that
22 # is the ideal way, imho
23 def for_simple (init=0,incr=1)
24 i = init
25 loop do
26 yield i
27 i += incr
28 end
29 end
30
31 # now let's test it
32 puts <<TEXT
33 Test I.
34 using our own simple for()... note advantage,
35 we don't need to track the counter...
36 TEXT
37
38 for_simple do |i|
39 break unless i*j/2 < maxnum
40 puts i
41 end
42
43 puts <<TEXT
44 Test II.
45 here we initialize to 2 and increment by 2
46 again, we don't need to track the counter...
47 TEXT
48
49 for_simple(2,2) do |i|
50 break unless i*j/2 < maxnum
51 puts i
52 end
53
54 puts <<TEXT
55 Test III.
56 again, here we initialize to 200 and decrement by 20
57 again, we don't need to track the counter...
58 and note, we change keyword unless to if
59 ruby just simply rocks..
60 TEXT
61
62 for_simple(200,-20) do |i|
63 break if i*j/2 < maxnum
64 puts i
65 end

C:\family\ruby>ruby test.rb
using while...
0
1
2
3
4
5
6
7
8
9
Test I.
using our own simple for()... note advantage,
we don't need to track the counter...
0
1
2
3
4
5
6
7
8
9
Test II.
here we initialize to 2 and increment by 2
again, we don't need to track the counter...
2
4
6
8
Test III.
again, here we initialize to 200 and decrement by 20
again, we don't need to track the counter...
and note, we change keyword unless to if
ruby just simply rocks..
200
180
160
140
120
100
80
60
40
20

C:\family\ruby>

Hth.
kind regards -botp

Michael W. Ryder

3/20/2007 6:57:00 PM

Peña wrote:
> From: Michael W. Ryder [mailto:_mwryder@worldnet.att.net] :
>
> # He would need to initialize i before your code as it could be
> # any value,
> # not just 0. By the same token the increment could be any number, not
> # just 1.
>
> fwiw, this is a simple example (intended for nubies only).
>
> C:\family\ruby>cat -n test.rb
> 1 #---------------------------
> 2 #emulate c++ for (the better)
> 3 #for(int i=0; i*j/2<maxNum; i++)
> 4 # {
> 5 # //cool method stuff
> 6 # }
> 7 #---------------------------
> 8
> 9 # using normal while loop
> 10 puts "using while..."
> 11 j=20
> 12 i=0
> 13 maxnum=100
> 14 while i*j/2 < maxnum do
> 15 puts i
> 16 i+=1
> 17 end
> 18
> 19 # let's make our own for() and call it for_simple :)
> 20 # note, there's no condition here
> 21 # we're leaving it up to yield/blocks since that
> 22 # is the ideal way, imho
> 23 def for_simple (init=0,incr=1)
> 24 i = init
> 25 loop do
> 26 yield i
> 27 i += incr
> 28 end
> 29 end
> 30
> 31 # now let's test it
> 32 puts <<TEXT
> 33 Test I.
> 34 using our own simple for()... note advantage,
> 35 we don't need to track the counter...
> 36 TEXT
> 37
> 38 for_simple do |i|
> 39 break unless i*j/2 < maxnum
> 40 puts i
> 41 end
> 42
> 43 puts <<TEXT
> 44 Test II.
> 45 here we initialize to 2 and increment by 2
> 46 again, we don't need to track the counter...
> 47 TEXT
> 48
> 49 for_simple(2,2) do |i|
> 50 break unless i*j/2 < maxnum
> 51 puts i
> 52 end
> 53
> 54 puts <<TEXT
> 55 Test III.
> 56 again, here we initialize to 200 and decrement by 20
> 57 again, we don't need to track the counter...
> 58 and note, we change keyword unless to if
> 59 ruby just simply rocks..
> 60 TEXT
> 61
> 62 for_simple(200,-20) do |i|
> 63 break if i*j/2 < maxnum
> 64 puts i
> 65 end
>
> C:\family\ruby>ruby test.rb
> using while...
> 0
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> Test I.
> using our own simple for()... note advantage,
> we don't need to track the counter...
> 0
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> Test II.
> here we initialize to 2 and increment by 2
> again, we don't need to track the counter...
> 2
> 4
> 6
> 8
> Test III.
> again, here we initialize to 200 and decrement by 20
> again, we don't need to track the counter...
> and note, we change keyword unless to if
> ruby just simply rocks..
> 200
> 180
> 160
> 140
> 120
> 100
> 80
> 60
> 40
> 20
>
> C:\family\ruby>
>
> Hth.
> kind regards -botp
>
>

Now is it possible, like in Scheme, to assign a variable to a string and
have Ruby evaluate the string? For example, f = "i*j/2". This would
allow one to make a more generic version of your methods. Ideally you
would have for_opt (i=0, f, inc=1) and have the method evaluate each of
the variables if necessary. This would allow one to copy working C code
without having to remember to do a lot of extraneous coding.

comp.lang.ruby

C(++) For Loop Equivalents

studlee2@gmail.com

Austin Ziegler

Raj Sahae

Michael W. Ryder

Peña, Botp

Michael W. Ryder

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