trinary: initial commit

cpp/trinary/README.md

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+# Trinary
+
+Write a program that will convert a trinary number, represented as a string (e.g. '102012'), to its decimal equivalent using first principles.
+
+The program should consider strings specifying an invalid trinary as the
+value 0.
+
+Trinary numbers contain three symbols: 0, 1, and 2.
+
+The last place in a trinary number is the 1's place. The second to last
+is the 3's place, the third to last is the 9's place, etc.
+
+```bash
+# "102012"
+    1       0       2       0       1       2    # the number
+1*3^5 + 0*3^4 + 2*3^3 + 0*3^2 + 1*3^1 + 2*3^0    # the value
+  243 +     0 +    54 +     0 +     3 +     2 =  302
+```
+
+If your language provides a method in the standard library to perform the
+conversion, pretend it doesn't exist and implement it yourself.
+
+## Getting Started
+
+Make sure you have read [the C++ page](http://exercism.io/languages/cpp) on
+exercism.io.  This covers the basic information on setting up the development
+environment expected by the exercises.
+
+## Passing the Tests
+
+Get the first test compiling, linking and passing by following the [three
+rules of test-driven development](http://butunclebob.com/ArticleS.UncleBob.TheThreeRulesOfTdd).
+Create just enough structure by declaring namespaces, functions, classes,
+etc., to satisfy any compiler errors and get the test to fail.  Then write
+just enough code to get the test to pass.  Once you've done that,
+uncomment the next test by moving the following line past the next test.
+
+```C++
+#if defined(EXERCISM_RUN_ALL_TESTS)
+```
+
+This may result in compile errors as new constructs may be invoked that
+you haven't yet declared or defined.  Again, fix the compile errors minimally
+to get a failing test, then change the code minimally to pass the test,
+refactor your implementation for readability and expressiveness and then
+go on to the next test.
+
+Try to use standard C++11 facilities in preference to writing your own
+low-level algorithms or facilities by hand.  [CppReference](http://en.cppreference.com/)
+is a wiki reference to the C++ language and standard library.  If you
+are new to C++, but have programmed in C, beware of
+[C traps and pitfalls](http://www.slideshare.net/LegalizeAdulthood/c-traps-and-pitfalls-for-c-programmers).
+
+## Source
+
+All of Computer Science [view source](http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-)