merge libmaple docs ("leaflabs-docs") into ./docs

In the past, libample documentation was forked out of this repository
because the documentation had increased in scope. For the librambutan,
and the rambutan project in general, we will try to keep documentation
closer to the source code, so the librambutan-specific documentation
should live here. Other sections of leaflabs-docs will be culled in a
following commit.

This merge attempts to maintain history by using a subtree strategy.
Followed directions at:

    http://nuclearsquid.com/writings/subtree-merging-and-you/

Full history for files should be accessible using the "--follow" flag to
git log, eg:

    git log --follow docs/source/adc.rst

It should be possible to pull patches from leaflabs-docs with:

    git pull -s subtree leaflabs-docs master

... at least until the docs in this repository diverge significantly.

1 files changed, 121 insertions, 0 deletions

diff --git a/docs/source/lang/cpp/if.rst b/docs/source/lang/cpp/if.rst
new file mode 100644
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+.. highlight:: cpp
+
+.. _lang-if:
+
+``if``/``else``
+===============
+
+An ``if`` statement is used to execute code when certain conditions
+are met.  The general syntax for an ``if`` statement is::
+
+    if (condition) {
+        body
+    }
+
+An ``if`` statement first tests whether its *condition* is true (such
+as an input being above a certain number).  If the condition is true,
+the ``if`` statement executes its *body*, which is made up of lines of
+code inside :ref:`curly braces <lang-curly-braces>`.  If the condition
+is false, the body is not executed.  Here's a more concrete example::
+
+    if (someVariable > 50) {
+      // do something here
+    }
+
+The program tests to see if ``someVariable`` is greater than 50. If it
+is, the program executes every line in the curly braces (which in the
+above example does nothing, since the body is just the :ref:`comment
+<lang-comments>` line "``// do something here``").
+
+Put another way, if the statement in parentheses is true, the
+statements inside the braces are run. If not, the program skips over
+the code.
+
+An ``if`` statement's condition (which is inside the parentheses after
+``if``) often uses one or more :ref:`boolean <lang-boolean>` or
+:ref:`comparison <lang-comparison>` operators.
+
+Writing the if Body
+-------------------
+
+The brackets may be omitted after an ``if`` statement's
+conditional. If this is done, the next line (which ends in a
+semicolon) becomes the only line in the body.  The following three
+``if`` statements all do the same thing::
+
+    if (x > 120) digitalWrite(pin, HIGH);
+
+    if (x > 120)
+        digitalWrite(pin, HIGH);
+
+    if (x > 120) {
+        digitalWrite(pin, HIGH);
+    }
+
+However, the following two examples are different::
+
+    // example 1: two lines of code in the if body
+    if (x > 120) {
+      digitalWrite(pin1, HIGH);
+      digitalWrite(pin2, HIGH);
+    }
+
+    // example 2: one line of code in the if body, and
+    // another line of code after the if statement
+    if (x > 120)
+      digitalWrite(pin1, HIGH); // this is in the if body
+      digitalWrite(pin2, HIGH); // this is NOT in the if body
+
+In the first example, since the body is enclosed in curly braces, both
+lines are included.  In the second example, since the curly braces are
+missing, only the first line is in the ``if`` body.
+
+``else``
+--------
+
+``if``/\ ``else`` allows greater control over the flow of code than
+the basic :ref:`if <lang-if>` statement, by allowing multiple tests to
+be grouped together. For example, an :ref:`analog input
+<lang-analogread>` could be tested, with one action taken if the input
+was less than 500, and another action taken if the input was 500 or
+greater. The code would look like this::
+
+    if (pinFiveInput < 500) {
+      // action A
+    } else {
+      // action B
+    }
+
+``else`` can precede another ``if`` test, so that multiple, mutually
+exclusive tests can be run at the same time.
+
+Each test will proceed to the next one until a true test is
+encountered. When a true test is found, its associated block of code
+is run, and the program then skips to the line following the entire
+if/else construction. If no test proves to be true, the default
+``else`` block is executed, if one is present, and sets the default
+behavior.
+
+Note that an ``else if`` block may be used with or without a
+terminating ``else`` block, and vice-versa. An unlimited number of
+such ``else if`` branches is allowed.  Here is a code example::
+
+    if (pinFiveInput < 500) {
+      // do Thing A
+    } else if (pinFiveInput >= 1000) {
+      // do Thing B
+    } else {
+      // do Thing C
+    }
+
+Another way to express branching, mutually exclusive tests, is with a
+:ref:`switch/case <lang-switchcase>` statement.
+
+
+See Also
+--------
+
+- :ref:`boolean operators <lang-boolean>`
+- :ref:`comparison operators <lang-comparison>`
+
+.. include:: /arduino-cc-attribution.txt