OpenEuphoria

RE: Converting a string to a variable name

• Posted by Derek Parnell <Derek.Parnell at SYD.RABOBANK.COM> Jul 28, 2002
• 474 views

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I know a lot of people have already responded to this, but may I add my
slant too.

> -----Original Message-----
> From: rubis at fem.unicamp.br [mailto:rubis at fem.unicamp.br]
> Subject: Converting a string to a variable name
> 
> 
> 
> Hi all;
> 
> Direct to the point...
> 
> 	I'm writing a program that uses a lot of sequencial variables:
> 
> a1, a2, a3...

And here is the key concept - 'sequential variables' - This is also known as
an array in programming term. In Euphoria, an array can be implemented using
a sequence.

Thus  'a1' is the first 'a', 'a2' is the second 'a', 'a3' is the third 'a',
etc...

So, if you know how many 'a's you need you can do this...

  sequence a
  a = repeat(0, maxA)

> and give values for then:
> 
> a1=1, a2=2, a3=3 ...(for example)
> 

  a[1] = 1
  a[2] = 2
  a[3] = 3

> I would like to do this:
> 
> atom a1,a2,a3
> sequence s
> 	for x=1 to 3 do
> 
> 		s=sprintf("%d",x)
> 		"a"&s=x                           -- atribute a 

    for x = 1 to length(a) do
        a[x] = x
    end for

> "variable variable" name 
> a variable value  :>))
> 
> 	end for
> 
> but this does not work because "a"&s is a string, not a variable.
> 
> How I can convert a string to a variable name ???

If you are using sequential variables, you don't have to.

Another type of array, is one where the elements are NOT sequential. That
is, the elements are not referenced by number, but by something else - a
string for example.

  a["ant"] = 1
  a["bat"] = 2
  a["kat"] = 3
  a["dog"] = 4
     ... etc...

Unfortunately, Euphoria doesn't directly support this idea. However, it can
support it indirectly.

  sequence names
  sequence a

   names = {"ant", "bat", "kat", "dog"}
   a = repeat(0, length(names))
 
  a[find("ant", names)] = 1
  a[find("bat", names)] = 2
  a[find("kat", names)] = 3
  a[find("dog", names)] = 4


  --To add a new named element...
   names = append(names, "emu")
   a     = append(a,     0)

The above is alright so long as you always use the correct names. As a
simple trick to cater for wrong names being used...


  sequence names
  sequence a

   names = {"ant", "bat", "kat", "dog"}
   a = repeat(0, length(names) + 1) -- Add an extra to handle bad names.
 
  a[find(The_Name, names) + 1] = New_Value

The '+ 1' is used so that if the value in The_Name is not a valid name, then
the first element is assigned. If the name is valid then its correct
position is assigned - the first name uses the second 'a', the second name
uses the third 'a', etc...

Alternatively, you might do it this way...
   integer idx

   idx = find(The_Name, names)
   if idx then
       a[idx] = New_Value
   else
       errmsg "Wrong name used"
   end if

---------------
hth,
Derek


   

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