# Variable value by its name representation as string

I am stuck at the stupidest problem - can not figure out how to get variable value. See the code below

```5 a(1)=2:b(1)=10:c(1)=100
10 data "a","b","c"
15 restore 10
20 for i=0 to 2
40 x=... ???
50 print x
60 next i
```

I define list of variable names using DATA, each of these variables are arrays. I need to take value of a(1) according to read of first string from data, b(1) according to reading second, etc. What ...??? must be to convert a\$ being "a" to value of a(1)?

I have a suspicion that it may simply be impossible at BASIC level. Please advise.

Aangemeld of registreer om reacties te plaatsen

i deleted line 5 and put its value in line 10 as string, so between quotes. then line 40 became x=val(a\$). That gave the following output:
2
10
100

i don't expect the variables in line 5 will go into the strings in line 10.

I am not an expert with BASIC, but I'd say it is not possible for a BASIC program to evaluate a string as an expression.

I don't know if i am saying something wrong, but i would convert the "a" in the ascii code with the ASC command and then evaluate the result with an if. Too long way?

Indeed, strings can't be evaluated as variable names, as far as I know

I guess it should possible by calling some basic interpreter functions, like in the thread below:
https://www.msx.org/forum/msx-talk/development/invoking-the-...

It's easier to just use one multidimensional array and change the data to indexes.

Nothing really to add here, I think Arjan covered your options... MSX-BASIC does not natively have anything like EXECUTE-command.

Working version of your listing would be:

```1 dim d(2,10)
5 d(0,1)=2:d(1,1)=10:d(2,1)=100
10 data 0,1,2
15 restore 10
20 for i=0 to 2
40 x=d(p,1)
50 print x
60 next i
```

«VAL» could be your friend, Eugeny, but on ZX Spectrum. Usage like «x=val(a\$+"(1)")» would evaluate an expression. Unfortunately, MSX BASIC parses numbers only. I am in search for solution for same problem, but also I want to assign variables given by a name in string variable. I have some kind of tricky solution as self-modifying BASIC program, but I hope there is more natural ways.

UPD: https://www.msx.org/wiki/VARPTR() should work both directions, if only you can interpret bytes of how variable stored. I think it is enough for my task, hence I needed this for integers only, but maybe will be useful for you too.

Or `if a\$="a" then x=a(1) else if a\$="b" then x=b(1) else x=c(1)`.

This might become too long for all possible 1-letter variables. But MSX-BASIC supports two-letter variables also. It multiplicates with different suffixes for different variable types, but even without we can probably go out of available program RAM, not talking about just fingers wear off typing it.
By the way, I just tried my variant and it definitely won't work: VARPTR accepts var itself, not a quoted name. So I will examine how variables work on low level.

Well, I don't recommend it, but if you absolutely must, here's my solution:

```40 defusr5=&hd000:x=usr5(a\$+"(1)")
```

With this relocatable routine loaded at 0D000h:

```ERRBAS		equ	406Fh
;PTRGET		equ	4E9Bh
PTRGET		equ	5EA4h
VMOVFM		equ	2F08h
VALTYP		equ	0F663h
DAC		equ	0F7F6h

ld	a,(VALTYP)
cp	3
jr	nz,ErrD
ld	de,(DAC+2)
ld	hl,0E9E1h
ld	(DAC+2),hl
call	DAC+2
ld	bc,buf-\$
ex	de,hl
ld	(DAC+2),hl
ld	b,(hl)
xor	a
cp	b
jr	z,Err18
inc	hl
ld	a,(hl)
inc	hl
ld	h,(hl)
ld	l,a
push	de
UpperLoop:	ld	a,(hl)
inc	hl
cp	'a'
jr	c,NotLower
cp	'z'+1
jr	nc,NotLower
NotLower:	ld	(de),a
inc	de
djnz	UpperLoop
xor	a
ld	(de),a
pop	hl
call	PTRGET
ex	de,hl
ld	(DAC+2),hl
rst	28h
call	nz,VMOVFM
ret
ErrD:		ld	e,0Dh
jp	ERRBAS
Err18:		ld	e,18h
jp	ERRBAS

buf:		ds	256
```

It takes 336 bytes and lets you examine any variable.