Tutorial:ForLoopsandWhileLoopsPublishDate:Apr01,2015

OverviewThistutorialexploressomeofthebasicfunctionsandusesofForLoopsandWhileLoops.YouwilllearnhowtocreateForLoopsandWhileLoopsandwhentheappropriatetimewouldbetousetheminyourprogram.

TableofContents

AwhileloopisacontrolflowstatementyouusetoexecuteablockofthesubdiagramcoderepeatedlyuntilagivenBooleanconditionismet.First,youexecutethecodewithinthesubdiagram,andthentheconditionalterminalisevaluated.Unlikeaforloop,awhileloopdoesnothaveasetiterationcountthus,awhileloopexecutesindefinitelyiftheconditionneveroccurs.

Aforloopisacontrolflowstatementyouusetoexecuteablockofthesubdiagramcodeasetnumberoftimes,butawhileloopstopsexecutingthesubdiagramonlyifthevalueattheconditionalterminalexists.

BuildingaWhileLoop

1.OpenanewVI.YoucanopenablankVIbyselectingFileNewVI2.IftheFunctionspaletteisnotvisible,rightclickanyblankspaceontheblockdiagramtodisplayatemporaryversionofthepalette.ClickthethumbtackintheupperleftcorneroftheFunctionspalettetopinthepalettesoitisnolongertemporary.3.SelectthewhileloopfromtheStructurespaletteundertheFunctionspalette.

4.Usethecursortodragaselectionrectanglearoundthesectionoftheblockdiagramyouwanttorepeat.

5.Whenyoureleasethemousebutton,awhileloopboundaryenclosesthesectionyouhaveselected.

6.PlaceaStopbuttononthefrontpanel.YoucanfindthisunderControlsPaletteBooleanStop.

7.AddtheStopbuttonfromtheblockdiagramtothewhileloopbydragginganddroppingitinsidethewhileloop.

8.Theconditionalterminal,shownbelow,defineswhentheloopstops.Therearetwosettingsfortheconditionalterminal:ContinueifTrueandStopifTrue.WhensettoContinueifTrue,thewhilelooprunsonlyifaBooleanvalueoftrueissenttotheterminal.IftheconditionalterminalissettoStopifTrue,andaBooleanvalueoftrueissenttotheconditionalterminal,theloophaltsexecution.

StopifTrue

ContinueifTrue

9.ToswitchtheconditionalterminalbetweenContinueifTrueandStopifTrue,rightclickontheconditionalterminalandcheckthecorrespondingsetting.

10.WiretheStopbuttontotheconditionalterminalsothatyoucancontroltheexecutionofthewhileloop.WhentheStopbuttonispressed,atruevalueispassedtotheconditionalterminalcausingthewhilelooptostopexecution.YoucanwireanyBooleandatatotheconditionalterminaltocontroltheexecutionofawhileloop.

11.Theiterationterminalisanoutputterminalthatcontainsthenumberofcompletediterations.Theiterationcountalwaysstartsatzero.Duringthefirstiteration,theiterationterminalreturns0.

12.YouhavejustcreatedasimplewhileloopthatgeneratesrandomnumbersanddisplaysthemuntiltheStopbuttonispressed.

StructureTunnels

Usestructuretunnelstofeeddataintoandoutofstructureslikethewhileloop.Ifyouwanttosenddataintoyourwhileloop,youneedtocreatestructuretunnels.DatasentintotheWhileLoopissentonlyonthefirstiteration,anddatasentoutofthewhileloopissentonlyafterthelastiteration.Nowcreateastructuretunneltodisplaythenumberofiterationsexecuted.

1.Createanumericindicatoronthefrontpanel.

2.Dragadatawirefromtheiterationcounterintotheborderofthewhilelooptocreateastructuretunnel.

3.Thetunnelappearsasasolidblockontheborderofthewhileloop.Theblockisthecolorofthedatatypewiredtothetunnel.Datapassoutofaloopaftertheloopterminates.Whenatunnelpassesdataintoaloop,theloopexecutesonlyafterdataarriveatthetunnel.

4.Dragadatawirefromthestructuretunnelintothenumericindicatortopassthenumberofiterationstoyourdisplay.

5.Inthefollowingblockdiagram,theiterationterminalisconnectedtoatunnel.Thevalueinthetunneldoesnotgetpassedtotheiterationindicatoruntilthewhileloopfinishesexecuting.

ManipulatingtheConditionalTerminal

ByusingBooleanfunctions,youcanimplementmultipleconditionstoaffectyourwhileloopconditionalterminal.YoucanuseanorfunctiontocompareanerrorwirestatusandaStopbuttoncontrolsothatifeitherisTRUE,theconditionalterminalreceivesaTRUEsignal,andthewhileloopstops.

1.Createawhileloopasoutlinedpreviously.

2.PlaceanErrorIn3D.ctlcontrolonthefrontpanel.YoucanfindthisunderControlsPaletteArray,Matrix&ClusterErrorIn3D.ctl.

3.RemovetheconnectionwirebetweentheStopbuttonandtheconditionalterminal.4.MakesuretheErrorIn3D.ctlisoutsideofthewhileloop.5.PlaceaSimpleErrorHandleroutsideofthewhileloop.YoucanfindthisunderFunctionsPaletteDialog&UserInterfaceSimpleErrorHandler.vi.Thisfunctionreportsanyerrorsencounteredwhencalled.

6.LinktheerrorincontrolwiththeSimpleErrorHandlerthroughthewhileloopviastructuretunnels.Dragawirefromtheoutputoftheerrorincontroltotheborderofthewhileloop,andthendragtheerrorwirefromthetunnelcreatedtotheoppositeborderofthewhileloopandintotheinputoftheSimpleErrorHandler.

7.PlaceanUnbundleByNamefunctioninsideofthewhileloop.YoucanfindthisunderFunctionsPaletteProgrammingCluster,Class,&Variant.ThisfunctionseparatestheBooleanportionoftheerrordatawire.

8.Placeanorfunctioninsideofthewhileloop.YoucanfindthisunderFunctions

PaletteProgrammingBoolean.

9.Linkthedatawiresasshownbelow.ThissimpleVIstopsexecutionofthewhileloopifeithertheStopbuttonispressedoranerrorisdetectedinsideofthewhileloop.

BuildingaForLoop

1.OpenanewVI.YoucanopenablankVIbyselectingFileNewVI.2.IftheFunctionspaletteisnotvisible,rightclickanyblankspaceontheblockdiagramtodisplayatemporaryversionoftheFunctionspalette.ClickthethumbtackintheupperleftcorneroftheFunctionspalettetopinthepalettesoitisnolongertemporary.3.SelecttheforloopfromtheStructurespaletteundertheFunctionspalette.

4.Youalsocanplaceawhileloopontheblockdiagram.RightclicktheborderofthewhileloopandselectReplacewithForLoopfromtheshortcutmenutochangeawhilelooptoaforloop.

5.Aforloopcontainsacountterminal.Thecountterminaldictateshowmanytimesthesubdiagramisexecuted.6.RightclickonthecountterminalandCreateConstanttolinkthecountterminalwithanumericvalue.

7.Byinserting100intothenumericconstant,theforloopexecutes100timesbeforestopping.

8.Theiterationterminal,shownasfollows,isanoutputterminalthatcontainsthenumberofcompletediterations.Theexamplebelowwouldupdateanindicatoronthefrontpanelwiththecurrentiterationnumber.

AddingaConditionalTerminaltoaForLoop

Ifnecessary,youcanaddaconditionalterminaltoconfigureaforlooptostopwhenaBooleanconditionoranerroroccurs.1.RightclickontheedgeoftheforloopandselectConditionalTerminal.

2.Aforloopwithaconditionalterminalexecutesuntiltheconditionoccursoruntilalliterationsarecomplete,whicheverhappensfirst.3.Forloopsyouconfigureforaconditionalexithavearedglyphinthecountterminalaswellasaconditionalterminalinthelowerrightcorner.

4.Afteryouconfiguretheforlooptoexitconditionally,theloopappearssimilartothefigurebelow.Thefollowingforloopgeneratesarandomnumbereveryseconduntil100secondshaspassedortheuserclickstheStopbutton.

Formoreinformationontheusesofforloopsandwhileloops,refertotheContextHelp.YoucanaccessContextHelpfromHelpShowContextHelporusingtheshortcut.

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