Re: simple question if/while loop

*To*: mathgroup at smc.vnet.net*Subject*: [mg40115] Re: simple question if/while loop*From*: atelesforos at hotmail.com (Orestis Vantzos)*Date*: Fri, 21 Mar 2003 02:36:44 -0500 (EST)*References*: <b5bk79$5t4$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

a:=Random[] is a 'delayed' assignment which means that a will give a new random number every time it is called. Hence a>.5 will test one number but tb[[n]]=a will store another! Use a=Random[] instead and move it inside the While. By the way your code is a very bad example of Mathematica programming; Mathematica is better programmed using list operations, like Join, Inner, etc. It's better to begin with an empty list tb={} and just add the new elements using Join. I would recommend something like the following: TestListFun[]:=Module[{a,tb,n}, tb = {}; n = 1; While[ n<5, a = Random[]; If[ a>.5, Join[tb,{a}];n++]; (* no need for Continue[] *) ]; tb ] Realizing that n is just the length of the list we can just use the following: TestListFun2[]:=Module[{tb,a}, tb = {}; While[ Length[tb]<4, a = Random[]; If[a>.5, Join[tb,{a}]]; ] tb ] Finally the functional approach: NestWhile[ Module[{a}, If[(a = Random[]) > .5, Join[#, {a}], #]] &, {}, Length[#] < 4 & ] will return what you want. Orestis s kp <kpsj2002 at yahoo.com> wrote in message news:<b5bk79$5t4$1 at smc.vnet.net>... > I am trying to do the following for a test purpose so I am a learning mathematica > > TestFun[] := Module[{a, tb, n}, > tb = Table[0.0, {4}]; > n := 1; > a := Random[]; > While[n < 5, > If[ a > .5, > (tb[[n]] = a; > n++;), Continue[] > ] > ] > tb > ] > > The output that I get is > > {0.871577 Null, 0.512558 Null, 0.00441806 Null, 0.520545 Null} > > Why am I doing wrong here and what is the correct way to do the above thing using If and While loop? > > thanks