Saturday, September 25, 2010


Summary: In this section, you will learn about Auto-Indexing.

If you wire an array to a For Loop or While Loop input tunnel, you can read and process every element in that array by enabling auto-indexing. When you auto-index an arrayoutput tunnel, the output array receives a new element from every iteration of the loop. The wire from the output tunnel to the array indicator becomes thicker as it changes to an array at the loop border, and the output tunnel contains square brackets representing an array, as shown in Figure 1.
Figure 1
Figure 1 (autoindexon.png)
Disable auto-indexing by right-clicking the tunnel and selecting Disable Indexing from the shortcut menu. For example, disable auto-indexing if you need only the last value passed to the tunnel in the previous example.
Because you can use For Loops to process arrays an element at a time, LabVIEW enables auto-indexing by default for every array you wire to a For Loop and for each output tunnel that is created. Auto-indexing for While Loops is disabled by default. To enable auto-indexing, right-click a tunnel and select Enable Indexing from the shortcut menu.

Creating Two-Dimensional Arrays

You can use two For Loops, one inside the other, to create a 2-D array. The outer For Loop creates the row elements, and the inner For Loop creates the column elements, as shown in Figure 2.
Figure 2
Figure 2 (2darrayforloop.png)

Using Auto-Indexing to Set the For Loop Count

If you enable auto-indexing on an array wired to a For Loop input terminal, LabVIEW sets the count terminal to the array size so you do not need to wire the count terminal.
In Figure 3, the For Loop executes a number of times equal to the number of elements in the array. Normally, if the count terminal of the For Loop is not wired, the run arrow is broken. However, in this case the run arrow is not broken.
Figure 3
Figure 3 (autoindexinput.png)
If you enable auto-indexing for more than one tunnel or if you wire the count terminal, the count changes to the smaller of the two. For example, if you wire an array with 10 elements to a For Loop input tunnel and you set the count terminal to 15, the loop executes only 10 times.

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