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st: -exit- within -forvalues- loop


From   "Stephen P. Jenkins" <stephenj@essex.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: -exit- within -forvalues- loop
Date   Tue, 22 Nov 2005 15:17:21 +0000

I am checking a condition within a -forvalues- loop, with the idea that if the
condition fails, the program will be stopped using -exit-.  I found some
unexpected behaviour with one set of code ("version 1" below). "Version 2"
produced the expected behaviour.  Note that version 1 code gets through ok to
the "Hello World" display command (which I hadn't expected), whereas the
version 2 code stops before that display command.

Advice please concerning why "version 1" works as it does, together with any
related tips on the code.

I note from online help for -exit- that "More generally, exit causes Stata to
terminate the current process and return control to the calling process." Is it
that the return in the version 1 case was to one level higher, i.e. outside the
loop?  Or something like that?  (I don't have access to manuals at present.)

thanks
Stephen

Here follows code and then output from using it. (Same results in version 8.2
and version 9.1)
++++++++++++++++++++++++++++++++++++++++++++++++

// D is exact multiple of both primes

local M = 2

tempname primes
mat `primes' = (3, 5)

local D = 15

***** version 1 ***********

forval i = 1/`M' {
	local prime = `primes'[1,`i']
	if mod(`D',`prime') == 0 {
		di as err "{p 0 0 4}Number of draws should not "
		di as err "be exact multiple of chosen prime. "
		di as err "(Problem is for equation `i' "
		di as err "and prime `prime'.){p_end}"
		exit
	}
}
di "hello world #1"



***** version 2 ***********
forval i = 1/`M' {
	local prime = `primes'[1,`i']
	if mod(`D',`prime') == 0 {
		di as err "{p 0 0 4}Number of draws should not "
		di as err "be exact multiple of chosen prime. "
		di as err "(Problem is for equation `i' "
		di as err "and prime `prime'.){p_end}"
		local y = 1
	}
}
if `y' == 1 exit
di "hello world #2"

+++++++++  output +++++++++++++++++++++++++++++++++++++++++++++++++++

. // D is exact multiple of both primes
.
. local M = 2

.
. tempname primes

. mat `primes' = (3, 5)

.
. local D = 15

.
. ***** version 1 ***********
.
. forval i = 1/`M' {
  2.         local prime = `primes'[1,`i']
  3.         if mod(`D',`prime') == 0 {
  4.                 di as err "{p 0 0 4}Number of draws should not "
  5.                 di as err "be exact multiple of chosen prime. "
  6.                 di as err "(Problem is for equation `i' "
  7.                 di as err "and prime `prime'.){p_end}"
  8.                 exit
  9.         }
 10. }
Number of draws should not be exact multiple of chosen prime.  (Problem is for
equation 1 and
prime 3.)
Number of draws should not be exact multiple of chosen prime.  (Problem is for
equation 2 and
prime 5.)

. di "hello world #1"
hello world #1

.
.
.
. ***** version 2 ***********
. forval i = 1/`M' {
  2.         local prime = `primes'[1,`i']
  3.         if mod(`D',`prime') == 0 {
  4.                 di as err "{p 0 0 4}Number of draws should not "
  5.                 di as err "be exact multiple of chosen prime. "
  6.                 di as err "(Problem is for equation `i' "
  7.                 di as err "and prime `prime'.){p_end}"
  8.                 local y = 1
  9.         }
 10. }
Number of draws should not be exact multiple of chosen prime.  (Problem is for
equation 1 and
prime 3.)
Number of draws should not be exact multiple of chosen prime.  (Problem is for
equation 2 and
prime 5.)

. if `y' == 1 exit

end of do-file

.


--
Professor Stephen P. Jenkins <stephenj@essex.ac.uk>
Institute for Social and Economic Research (ISER)
University of Essex, Colchester, CO4 3SQ, UK
Tel: +44 (0)1206 873374. Fax: +44 (0)1206 873151.
http://www.iser.essex.ac.uk
Survival Analysis using Stata:
http://www.iser.essex.ac.uk/teaching/degree/stephenj/ec968/

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