Implement armstrong numbers

config.json

@@ -543,6 +543,18 @@
         "math",
         "strings"
       ]
+    },
+    {
+      "slug": "armstrong-numbers",
+      "uuid": "1035aa3f-030a-425b-84f1-1967f344d155",
+      "core": false,
+      "unlocked_by": null,
+      "difficulty": 3,
+      "topics": [
+        "algorithm",
+        "loops",
+        "math"
+      ]
     }
   ]
 }

exercises/armstrong-numbers/CMakeLists.txt

@@ -0,0 +1,53 @@
+# Get the exercise name from the current directory
+get_filename_component(exercise ${CMAKE_CURRENT_SOURCE_DIR} NAME)
+
+# Basic CMake project
+cmake_minimum_required(VERSION 3.1.3)
+
+# Name the project after the exercise
+project(${exercise} CXX)
+
+# Get a source filename from the exercise name by replacing -'s with _'s
+string(REPLACE "-" "_" file ${exercise})
+
+# Implementation could be only a header
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${file}.cpp)
+    set(exercise_cpp ${file}.cpp)
+else()
+    set(exercise_cpp "")
+endif()
+
+# Use the common Catch library?
+if(EXERCISM_COMMON_CATCH)
+    # For Exercism track development only
+    add_executable(${exercise} ${file}_test.cpp ${exercise_cpp} ${file}.h $<TARGET_OBJECTS:catchlib>)
+else()
+    # Build executable from sources and headers
+    add_executable(${exercise} ${file}_test.cpp ${exercise_cpp} ${file}.h test/tests-main.cpp)
+endif()
+
+set_target_properties(${exercise} PROPERTIES
+    CXX_STANDARD 11
+    CXX_STANDARD_REQUIRED OFF
+    CXX_EXTENSIONS OFF
+)
+
+if("${CMAKE_CXX_COMPILER_ID}" MATCHES "(GNU|Clang)")
+    set_target_properties(${exercise} PROPERTIES
+        COMPILE_FLAGS "-Wall -Wextra -Wpedantic -Werror"
+    )
+endif()
+
+# Configure to run all the tests?
+if(${EXERCISM_RUN_ALL_TESTS})
+    target_compile_definitions(${exercise} PRIVATE EXERCISM_RUN_ALL_TESTS)
+endif()
+
+# Tell MSVC not to warn us about unchecked iterators in debug builds
+if(${MSVC})
+    set_target_properties(${exercise} PROPERTIES
+        COMPILE_DEFINITIONS_DEBUG _SCL_SECURE_NO_WARNINGS)
+endif()
+
+# Run the tests on every build
+add_custom_target(test_${exercise} ALL DEPENDS ${exercise} COMMAND ${exercise})

exercises/armstrong-numbers/README.md

@@ -0,0 +1,51 @@
+# Armstrong Numbers
+
+An [Armstrong number](https://en.wikipedia.org/wiki/Narcissistic_number) is a number that is the sum of its own digits each raised to the power of the number of digits.
+
+For example:
+
+- 9 is an Armstrong number, because `9 = 9^1 = 9`
+- 10 is *not* an Armstrong number, because `10 != 1^2 + 0^2 = 1`
+- 153 is an Armstrong number, because: `153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153`
+- 154 is *not* an Armstrong number, because: `154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`
+
+Write some code to determine whether a number is an Armstrong number.
+
+## Getting Started
+
+Make sure you have read the [Installing](https://exercism.io/tracks/cpp/installation) and
+[Running the Tests](https://exercism.io/tracks/cpp/tests) pages for C++ 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
+
+Wikipedia [https://en.wikipedia.org/wiki/Narcissistic_number](https://en.wikipedia.org/wiki/Narcissistic_number)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

exercises/armstrong-numbers/armstrong_numbers_test.cpp

@@ -0,0 +1,51 @@
+#include "test/catch.hpp"
+#include "armstrong_numbers.h"
+
+// Armstrong-numbers exercise test case data version 1.1.0
+
+TEST_CASE("zero_is_an_armstrong_number")
+{
+    REQUIRE(armstrong_numbers::is_armstrong_number(0));
+}
+
+#if defined(EXERCISM_RUN_ALL_TESTS)
+TEST_CASE("single_digit_numbers_are_armstrong_numbers")
+{
+    REQUIRE(armstrong_numbers::is_armstrong_number(5));
+}
+
+TEST_CASE("there_are_no_2_digit_armstrong_numbers")
+{
+    REQUIRE_FALSE(armstrong_numbers::is_armstrong_number(10));
+}
+
+TEST_CASE("three_digit_number_that_is_an_armstrong_number")
+{
+    REQUIRE(armstrong_numbers::is_armstrong_number(153));
+}
+
+TEST_CASE("three_digit_number_that_is_not_an_armstrong_number")
+{
+    REQUIRE_FALSE(armstrong_numbers::is_armstrong_number(100));
+}
+
+TEST_CASE("four_digit_number_that_is_an_armstrong_number")
+{
+    REQUIRE(armstrong_numbers::is_armstrong_number(9474));
+}
+
+TEST_CASE("four_digit_number_that_is_not_an_armstrong_number")
+{
+    REQUIRE_FALSE(armstrong_numbers::is_armstrong_number(9475));
+}
+
+TEST_CASE("seven_digit_number_that_is_an_armstrong_number")
+{
+    REQUIRE(armstrong_numbers::is_armstrong_number(9926315));
+}
+
+TEST_CASE("seven_digit_number_that_is_not_an_armstrong_number")
+{
+    REQUIRE_FALSE(armstrong_numbers::is_armstrong_number(9926314));
+}
+#endif // !EXERCISM_RUN_ALL_TESTS

exercises/armstrong-numbers/example.cpp

@@ -0,0 +1,11 @@
+#include "armstrong_numbers.h"
+#include <cmath>
+
+bool armstrong_numbers::is_armstrong_number(int number) {
+    int length = number != 0 && number != 1 ? std::log10(std::abs(number)) + 1 : 1;
+    int accumulate = 0;
+    for (int current = number; current != 0; current /= 10) {
+        accumulate += std::pow(current % 10, length);
+    }
+    return accumulate == number;
+}

exercises/armstrong-numbers/example.h

@@ -0,0 +1,10 @@
+#if !defined(ARMSTRONG_NUMBERS_H_)
+#define ARMSTRONG_NUMBERS_H_
+
+namespace armstrong_numbers {
+
+bool is_armstrong_number(int number);
+
+} // namespace armstrong_numbers
+
+#endif // !ARMSTRONG_NUMBERS_H_