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Code Editor : pic-16.html

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<h2>16. Control-flow constructs
<a name="16. Control-flow constructs"></a>
</h2>

The
pic language provides conditionals and looping. For
example,

pi
= atan2(0,-1); 
for i = 0 to 2 * pi by 0.1 do { 
&quot;-&quot; at (i/2, 0); 
&quot;.&quot; at (i/2, sin(i)/2); 
&quot;:&quot; at (i/2, cos(i)/2); 
}

which
yields this:

Figure
16-1: Plotting with a for loop

The syntax
of the for statement is:

for
variable = expr1 to expr2
[by [*]expr3] do X body
X

The
semantics are as follows: Set variable to
expr1. While the value of variable is less
than or equal to expr2, do body and increment
variable by expr3; if by is not given,
increment variable by&nbsp;1. If expr3 is
prefixed by&nbsp;* then variable is multiplied
instead by expr3. The value of expr3 can be
negative for the additive case; variable is then
tested whether it is greater than or equal to expr2.
For the multiplicative case, expr3 must be greater
than zero. If the constraints aren&rsquo;t met, the loop
isn&rsquo;t executed. X can be any character not
occurring in body; or the two Xs may be paired
braces (as in the sh command).

The syntax
of the if statement is as follows:

if
expr then X if-true X [else Y
if-false Y]

Its
semantics are as follows: Evaluate expr; if it is
non-zero then do if-true, otherwise do
if-false. X can be any character not occurring
in if-true. Y can be any character not
occurring in if-false.

Eithe or
both of the X or Y pairs may instead be
balanced pairs of braces ({ and&nbsp;}) as in the sh
command. In either case, the if-true may contain
balanced pairs of braces. None of these delimiters are seen
inside strings.

All the
usual relational operators my be used in conditional
expressions; ! (logical negation, not factorial),
&amp;&amp;, ||, ==, !=,
&gt;=, &lt;=, &lt;,
&gt;.

String
comparison is also supported using == and !=.
String comparisons may need to be parenthesized to avoid
syntactic ambiguities.
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Code Editor : pic-16.html