Re: st: scalars in loops

[Gary Longton <glongton@fhcrc.org>]

I believe the difference is that -which- takes an expression argument and 
-forvalues- does not.  Though variables and scalars can be used in expressions, 
they cannot usually be used directly in non-expression arguments.

However, the introduction of of the macro expansion operator (in Stata 8 ?)

       `=exp'

has made it easy to get around this, evaluating the expression, exp, and 
substituting a string result in its place.

eg. you could do this :

  tempname m1
  scalar `m1' = 5
  forvalues a = 1(1)`=`m1'' {
	  di "`a'"
  }

- Gary

Dimitriy V. Masterov wrote:


> Can someone please explain to me why one cannot use scalars to define the
> upper bound in a range of a forvalues loop. A forvalues loop with a local
> works,  a while loop with a scalar works, a while loop with a local works,
> but not a forvalues loop with a scalar. There seems to be nothing in the
> programming manual about this issue.
>
> This is the code for the examples above:
>
> tempname m1 m2
>
> scalar `m1'=5
> local `m2'=5
>
>
> forvalues a=1(1)``m2'' {
> 	di "`a'"
> }
>
> local a=1
> 	while `a'<=``m2'' {
> 		di "`a'"
> 	local a=`a'+1
> }
>
>
> local a=1
> 	while `a'<=`m1' {
> 		di "`a'"
> 	local a=`a'+1
> }
>
> forvalues a=1(1)`m1' {
> 	di "`a'"
> }
>
> I am using Stata 8.2 SE with XP.


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