1. For loop and a newbie
- Posted by jc at cknet.net
Mar 25, 2001
-
Last edited Mar 26, 2001
Hello, I'm not getting what I would expect out of the below For Do loop.
The For loop variable 'i' initializes at 3 as I would expect, however during
the first loop I would expect cmd[i] to be cmd[3] but it isn't, it starts at
cmd[1].
cmd = command_line()
for i = 3 to length(cmd)-2 do
vcommands = cmd[i]
vresult = atom(vcommands[1])
if vresult != 1 then
directions()
abort(0)
end if
end for
I want to skip the first two command line parameters as they contain path
data. It's as if there are two 'i' variables within the context of the same
For loop running independantly........tell me that's not what's
happening........ What am I missing?
TIA
Jim Chapman
2. Re: For loop and a newbie
Hi Jim,
>Hello, I'm not getting what I would expect out of the below For Do
>loop. The For loop variable 'i' initializes at 3 as I would expect,
>however during the first loop I would expect cmd[i] to be cmd[3]
>but it isn't, it starts at cmd[1].
Well a couple of things first. I'm not sure why you think that it starts at
cmd[1]. Is it because the 'directions()' routine never runs when you give no
command options? Also, I'm not actually sure if I understand what you are
trying to do. I guess you are trying to display some help text if no command
parameters were supplied.
Assuming this, I'd try the code here instead ...
cmd = command_line()
if length(cmd) < 3 then
directions()
abort(0)
end if
But now to explain what your code is actually doing...
>cmd =command_line()
This copies the words on the command line to the sequence 'cmd'
Assuming the command line was "abc def ghi" then cmd will be
{"ex.exe","myprog","abd","def","ghi"}
That is a list of 5 (five) elements. The first two are paths, and
the next three are the command line words.
>for i =3 to length(cmd)-2 do
This starts a loop. The first 'i' will be three and the last 'i' will be the
number of elements in cmd minus 2.
In our example this means that 'i' will range from 3 to 3 (5 - 2).
>vcommands =cmd[i]
This copies the i'th word into sequence 'vcommands'
>vresult =atom(vcommands[1])
This test the first element in vcommands to see if its an atom or not.
Because 'cmds' contains a list of words (strings) then all the elements of
each string is an atom, so this test will always be true. That is, the first
element of vcommands is always an atom (the first character in the word).
>if vresult !=1 then
This test that the examined character was an atom.
>directions()
This executes the directions() procedure.
>abort(0)
This exits the program.
>end if
>end for
So in a nutshell, your program will only test the commandline words if there
is at least 3 of them and it will never run the directions routine because
the first element of every word is always an atom.
>I want to skip the first two command line parameters as they contain
>path data. It's as if there are two 'i' variables within the context
>of the same For loop running independantly........tell me that's not
>what's happening........
That's not happening.
> What am I missing?
Not sure. Maybe still confused about what a sequence is?
cheers,
------
Derek Parnell
Melbourne, Australia
"To finish a job quickly, go slower."
3. Re: For loop and a newbie
On Mon, 26 Mar 2001, jc at cknet.net wrote:
> Hello, I'm not getting what I would expect out of the below For Do loop.
> The For loop variable 'i' initializes at 3 as I would expect, however during
> the first loop I would expect cmd[i] to be cmd[3] but it isn't, it starts at
> cmd[1].
>
> cmd command_line()
> for i 3 to length(cmd)-2 do
> vcommands cmd[i]
> vresult atom(vcommands[1])
> if vresult ! 1 then
> directions()
> abort(0)
> end if
> end for
>
It would be hard to beat Derek's fine reply, but I'm curious why you
are using atom(vcommands[1])?
The command line parameters are _always_ strings, so, even if
you type "ex myprog One 2 Three 4", each item is a string.
Suppose you want to separate the actual string parameters from
those which contain only a number;
Here's a test program that will display the parameters, and
decide if each is a number or not: Execute it with a mix of
parameters, something like this:
ex myprog One 2 Three 56 Nine "45"
include get.e
sequence cmd
object result
cmd = command_line()
for i = 1 to length(cmd) do
printf(1,"Command line parameter #%d was %s\n",{i,cmd[i]})
result = value(cmd[i])
if result[1] = GET_SUCCESS then
printf(1," Hey, parameter %d is a number = %d\n",{i,result[2]})
end if
end for
--
Regards,
Irv
