Exiting From Loops Early; Using System Functions - Crestron SIMPL+ Programming Manual

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Using System Functions

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30 • SIMPL+
this code, the value of this expression determines whether or not the code should be
executed again. Here lies the other difference between the while and do-until. The
while loop executes as long as the expression remains TRUE. A do-until loop
executes until an expression becomes TRUE.
When deciding which type of loop should be used, first understand that using any of
the three types of loops discussed here can solve many problems. However, one
particular loop is usually better suited for a given application than the others. As a
general rule of thumb, when the number of iterations the code should execute is
known, a for loop is preferred. A while or a do-until loop is ideal to execute a section
of code continuously based on the value of some expression.
Once a while or a do-until loop is determined suitable for a particular application, the
question becomes which one of the two should be used? Once again realize that
either one can usually accomplish the goal, but one type of loop may require less
coding or be more readable in some cases. The basic question to ask is whether or
not the loop needs to run through at least one time. If so, a do-until is the best choice.
If instead, the value of an expression should be checked, then use the while loop.

Exiting from Loops Early

All three loops discussed above have built-in ways to exit. The for loop exits when
the index variable reaches the stated maximum. The while loop exits when the
expression becomes FALSE. The do-until loop exits when the expression becomes
TRUE.
Sometimes programming tasks do not always fall neatly into place regarding loops
and it may be desirable (or necessary) to exit a loop prematurely. Consider the
following example.
INTEGER x,y;
for (x=3 to z)
{
y = y + x*3 – z*z;
if (y = 0)
break;
}
Notice that in most (if not all) cases, the need for the break statement could be
avoided by the use of a different type of loop. In the example above, this could be
accomplished by using a do-until loop. Consider the following.
x = 3;
do
{
y = y + x*3 – z*z;
x = x + 1;
} until ((y = 0) || (x = z))
Either technique would be considered acceptable.
In order to make programming in SIMPL+ simpler and more powerful, the concept
of functions is introduced. A function is essentially a more complicated
Crestron SIMPL+
Programming Guide – DOC. 5789A
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