Improves Hello-World (#279)

* Adding comments and a hello world example that compiles.

* Adding CI test for the compilable, but test failing, hello-world.

* Cleaning up hello().

* Improving include guard description.

Author: arcuru

.gitignore

@@ -11,3 +11,4 @@ cmake_install.cmake
 
 # Ignore alternate directory of exercises that is used for building
 build_exercises/
+build_hello-world/

.travis.yml

@@ -53,4 +53,5 @@ script:
   - bin/fetch-configlet
   - bin/configlet lint .
   - bin/check-configlet-fmt.sh
+  - bin/check-hello-world.sh
   - bin/check-exercises.sh

bin/check-hello-world.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+#
+# Test that the hello-world exercise compiles with no changes and fails.
+
+# Fail if any command fails
+set -e
+
+repo=$(cd "$(dirname "$0")/.." && pwd)
+
+hello_world_tmp_dir="$repo"/build_hello-world
+hello_world_dir="$repo"/exercises/hello-world
+
+mkdir -p "$hello_world_tmp_dir"
+
+cd "$hello_world_tmp_dir"
+
+# Configuring should work.
+cmake -G Ninja "$hello_world_dir"
+
+echo "Building hello-world, which should fail."
+
+# The build will fail, since it runs a failing test.
+if cmake --build .; then
+    # The build succeeded, which is not supposed to happen.
+    exit 1
+fi
+
+cd "$repo"

exercises/hello-world/example.cpp

@@ -4,7 +4,7 @@ using namespace std;
 
 namespace hello_world
 {
-	
+
 string hello()
 {
     return "Hello, World!";

exercises/hello-world/hello_world.cpp

@@ -0,0 +1,16 @@
+#include "hello_world.h"
+
+// Use everything from the 'std' namespace.
+// This lets us write 'string' instead of 'std::string'.
+using namespace std;
+
+namespace hello_world {
+
+// Define the function itself. This could have also been written as:
+// std::string hello_world::hello()
+string hello() {
+    // Return the string we need.
+    return "Fix me!";
+}
+
+}  // namespace hello_world

exercises/hello-world/hello_world.h

@@ -1,12 +1,22 @@
+// This is an include guard.
+// You could alternatively use '#pragma once'
+// See https://en.wikipedia.org/wiki/Include_guard
 #if !defined(HELLO_WORLD_H)
 #define HELLO_WORLD_H
 
+// Include the string header so that we have access to 'std::string'
 #include <string>
 
+// Declare a namespace for the function(s) we are exporting.
+// https://en.cppreference.com/w/cpp/language/namespace
 namespace hello_world {
 
+// Declare the 'hello()' function, which takes no arguments and returns a
+// 'std::string'. The function itself is defined in the hello_world.cpp source
+// file. Because it is inside of the 'hello_world' namespace, it's full name is
+// 'hello_world::hello()'.
 std::string hello();
 
-}
+}  // namespace hello_world
 
 #endif

exercises/hello-world/hello_world_test.cpp

@@ -1,7 +1,12 @@
+// Include the header file with the definitions of the functions you create.
 #include "hello_world.h"
+
+// Include the test framework.
 #include "test/catch.hpp"
 
+// Declares a single test.
 TEST_CASE("test_hello")
 {
-    REQUIRE("Hello, World!" == hello_world::hello());
+    // Check if your function returns "Hello, World!".
+    REQUIRE(hello_world::hello() == "Hello, World!");
 }