Propeller Manual

CASE – Spin Language Reference
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Using CASE
CASE is handy where one of many actions needs to be performed depending on the value of an
expression. The following example assumes
A, X and Y are variables defined earlier.
case X+Y 'Test X+Y
10, 15: !outa[0] 'X+Y = 10 or 15? Toggle P0
A*2 : !outa[1] 'X+Y = A*2? Toggle P1
30..40: !outa[2] 'X+Y in 30 to 40? Toggle P2
X += 5 'Add 5 to X
Since the MatchExpression lines are indented from the CASE line, they belong to the CASE
structure and are executed based on the CaseExpression comparison results. The next line,
X += 5, is not indented from CASE, so it is executed regardless of the CASE results.
This example compares the value of
X + Y against 10 or 15, A*2 and the range 30 through
40. If X + Y equals 10 or 15, P0 is toggled. If X + Y equals A*2, P1 is toggled. If X + Y is in
the range
30 through 40, inclusive, then P2 is toggled. Whether or not any match was found,
the
X += 5 line is executed next.
Using OTHER
The optional
OTHER component of CASE is similar to the optional ELSE component of an IF
structure. For example:
case X+Y 'Test X+Y
10, 15: !outa[0] 'X+Y = 10 or 15? Toggle P0
25 : !outa[1] 'X+Y = 25? Toggle P1
20..30: !outa[2] 'X+Y in 20 to 30? Toggle P2
OTHER : !outa[3] 'Otherwise toggle P3
X += 5 'Add 5 to X
This example is similar to the last one except that the third MatchStatement checks for the
range 20 to 30 and there’s an
OTHER component. If X + Y does not equal 10, 15, 25, or is not
in the range 20 to 30, the Statement(s) block following
OTHER is executed. Following that, the
X += 5 line is executed.
There is an important concept to note about this example. If
X + Y is 10 or 15, P0 is toggled,
or if
X + Y is 25, P1 is toggled, or if X + Y is 20 to 30, P2 is toggled, etc. This is because the
MatchExpressions are checked, one at a time, in the order they are listed and only the first
Page 60 · Propeller Manual v1.1