Add C++ implementation

cpp/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.4)
+project(theatrical_players_refactoring_kata)
+
+set(CMAKE_CXX_STANDARD 11)
+
+add_subdirectory(tests)

cpp/README.md

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+Theatrical Players Refactoring Kata - C++ version
+========================================================
+
+See the [top level readme](https://github.com/emilybache/Theatrical-Players-Refactoring-Kata) for general information about this exercise.
+
+## Dependencies
+
+The tests use the following header-only projects, which are in the `third_party` sub-directory:
+
+| Project | Licence |
+| --- | --- |
+| [doctest test framework](https://github.com/onqtam/doctest) | [MIT](https://github.com/onqtam/doctest/blob/master/LICENSE.txt) |
+| [ApprovalTests.cpp](https://github.com/approvals/ApprovalTests.cpp) | [Apache 2.0](https://github.com/approvals/ApprovalTests.cpp/blob/master/LICENSE) |
+| [JSON for Modern C++](https://github.com/nlohmann/json) | [MIT](https://github.com/nlohmann/json/blob/develop/LICENSE.MIT) |

cpp/statement.cpp

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+#include "statement.h"
+
+#include <iostream>
+#include <sstream>
+#include <iomanip>
+
+// https://stackoverflow.com/a/7277333/104370
+class comma_numpunct : public std::numpunct<char>
+{
+  protected:
+    virtual char do_thousands_sep() const override
+    {
+        return ',';
+    }
+
+    virtual std::string do_grouping() const override
+    {
+        return "\03";
+    }
+};
+
+std::string format_as_dollars(float amount)
+{
+    // this creates a new locale based on the current application default
+    // (which is either the one given on startup, but can be overriden with
+    // std::locale::global) - then extends it with an extra facet that 
+    // controls numeric output.
+    const std::locale comma_locale(std::locale(), new comma_numpunct());
+
+    std::ostringstream out;
+    // tell stream to use our new locale.
+    out.imbue(comma_locale);
+    out.precision(2);
+    out << "$" << std::fixed << amount;
+    return out.str();
+}
+
+std::string statement(
+    const nlohmann::json& invoice,
+    const nlohmann::json& plays)
+{
+    float total_amount = 0;
+    int volume_credits = 0;
+
+    std::stringstream result;
+    result << "Statement for " << invoice["customer"].get<std::string>() << '\n';
+
+    for( const auto& perf : invoice["performances"])
+    {
+        float this_amount = 0;
+        auto play = plays[perf["playID"].get<std::string>()];
+        if (play["type"] == "tragedy")
+        {
+            this_amount = 40000;
+            if (perf["audience"] > 30)
+            {
+                this_amount += 1000 * (perf["audience"].get<int>() - 30);
+            }
+        }
+
+        else if (play["type"] == "comedy")
+        {
+            this_amount = 30000;
+            if (perf["audience"] > 20)
+            {
+                this_amount += 10000 + 500 * (perf["audience"].get<int>() - 20);
+            }
+
+            this_amount += 300 * perf["audience"].get<int>();
+        }
+
+        else
+        {
+            throw std::domain_error("unknown type: " + play["type"].get<std::string>());
+        }
+
+        // add volume credits
+        volume_credits += std::max(perf["audience"].get<int>() - 30, 0);
+
+        // add extra credit for every ten comedy attendees
+        if ("comedy" == play["type"])
+        {
+            volume_credits += perf["audience"].get<int>() / 5;
+        }
+
+        // print line for this order
+        result << " " << play["name"].get<std::string>() << ": " << format_as_dollars(this_amount/100) << 
+            " (" << perf["audience"] << " seats)\n";
+        total_amount += this_amount;
+    }
+
+    result << "Amount owed is " << format_as_dollars(total_amount/100.0f) << "\n";
+    result << "You earned " << volume_credits << " credits";
+    return result.str();
+}

cpp/statement.h

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+// TODO Include Guard
+
+#include "json.hpp"
+
+std::string statement(
+    const nlohmann::json& invoice,
+    const nlohmann::json& plays);

cpp/tests/CMakeLists.txt

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+project(tests)
+
+add_executable(${PROJECT_NAME}
+    ../statement.cpp
+    ../statement.h
+    test_statement.cpp
+    main.cpp)
+
+target_include_directories(
+    ${PROJECT_NAME}
+    PUBLIC
+    ../third_party ..)
+
+enable_testing()
+add_test(NAME ${PROJECT_NAME}_test COMMAND ${PROJECT_NAME})

cpp/tests/main.cpp

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+#define APPROVALS_DOCTEST
+#include "ApprovalTests.hpp"

cpp/tests/test_statement.cpp

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+#include "statement.h"
+
+#include "json.hpp"
+#include "doctest.h"
+#include "ApprovalTests.hpp"
+
+#include <iostream>
+
+namespace
+{
+    std::string get_adjacent_file(const std::string& filename)
+    {
+        return ApprovalTestNamer().getDirectory() + filename;
+    }
+
+    nlohmann::json read_json_file(const std::string& filename)
+    {
+        std::ifstream invoice_stream(filename);
+        if ( ! invoice_stream.is_open())
+        {
+            std::cout << "Error opening file:" << filename << '\n';
+            std::cout << "Error: " << strerror(errno) << '\n';
+        }
+        nlohmann::json result;
+        invoice_stream >> result;
+        return result;
+    }
+}
+
+TEST_CASE("test_example_statement")
+{
+    auto invoice = read_json_file(get_adjacent_file("invoice.json"));
+    auto plays = read_json_file(get_adjacent_file("plays.json"));
+
+    Approvals::verify(statement(invoice, plays));
+}
+
+TEST_CASE("test_statement_with_new_play_types")
+{
+    auto invoice = read_json_file(get_adjacent_file("invoice_new_plays.json"));
+    auto plays = read_json_file(get_adjacent_file("new_plays.json"));
+    CHECK_THROWS_AS(statement(invoice, plays), std::domain_error);
+}