raindrops: initial commit

cpp/raindrops/README.md

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+# Raindrops
+
+Write a program that converts a number to a string, the contents of which depends on the number's prime factors.
+
+- If the number contains 3 as a prime factor, output 'Pling'.
+- If the number contains 5 as a prime factor, output 'Plang'.
+- If the number contains 7 as a prime factor, output 'Plong'.
+- If the number does not contain 3, 5, or 7 as a prime factor,
+  just pass the number's digits straight through.
+
+## Examples
+
+- 28's prime-factorization is 2, 2, 7.
+  - In raindrop-speak, this would be a simple "Plong".
+- 1755 prime-factorization is 3, 3, 3, 5, 13.
+  - In raindrop-speak, this would be a "PlingPlang".
+- The prime factors of 34 are 2 and 17.
+  - Raindrop-speak doesn't know what to make of that,
+    so it just goes with the straightforward "34".
+
+## Getting Started
+
+Make sure you have read the [getting started with C++](http://help.exercism.io/getting-started-with-cpp.html)
+page on the [exercism help site](http://help.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
+
+A variation on a famous interview question intended to weed out potential candidates. [view source](http://jumpstartlab.com)