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Repeats the code on its subdiagram until a specific condition occurs. A While Loop always executes at least one time. A While Loop behaves similarly to a do while loop in other programming languages.

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Iteration

Current loop iteration count. The loop count always starts at zero for the first iteration. If the iteration count exceeds 2,147,483,647, or 231-1, the iteration terminal remains at 2,147,483,647 for all further iterations. If you need to keep count of more than 2,147,483,647 iterations, you can use shift registers with a greater integer range.

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Condition

A Boolean input value to determine whether to continue executing the loop. To specify whether the loop stops for a TRUE or FALSE Boolean value, configure the continuation behavior. You also can determine when the loop stops by wiring an error cluster to the condition terminal.

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Tunnel

Point through which data enters or exits a structure.

In addition to this basic purpose, tunnels can assume the following functionalities:

  • Non-indexing tunnel—Passes the data through the loop border
  • Auto-indexing The behavior of an auto-indexing tunnel depends on whether it is an input or output tunnel. An auto-indexing input tunnel processes one element of an array for each iteration of the loop. An auto-indexing output tunnel appends a piece of data from a single loop iteration to an accumulating array of data. To turn on auto-indexing for a tunnel, click to highlight the Auto Index option in the Loop Tunnel group on the Tunnel Tools ribbon.
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Shift Register

Member of a pair of terminals that passes a value from one iteration of a loop to the next iteration. After the initial loop iteration, the left shift register in the pair returns the value it receives from the right shift register from the previous iteration. Refer to Accessing Data from the Previous Loop Iteration for more information about passing values from the previous iteration to the current iteration.