Merge branch 'master' into project_euler/master2

* master:
  set c99 standard as default
  checkout submodule as well
  use cd to build directory
  changed to checkout@master
  Create ccpp.yml

.github/workflows/ccpp.yml

@@ -0,0 +1,27 @@
+name: C/C++ CI
+
+on: [push]
+#   push:
+#     branches: [ master ]
+#   pull_request:
+#     branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix: 
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+
+    steps:
+    - uses: actions/checkout@master
+      with:
+        submodules: true
+    - name: build directory
+      run: mkdir build && cd build
+    - name: configure
+      run: cmake .
+    - name: build
+      run: cmake --build .
+      

CMakeLists.txt

@@ -13,6 +13,9 @@ include_directories(function_timer/include)
 # include_directories(${CMAKE_BINARY_DIR}/include)
 # link_directories(${CMAKE_BINARY_DIR}/lib/${CMAKE_BUILD_TYPE})
 
+set(CMAKE_C_STANDARD 99)
+set(CMAKE_C_STANDARD_REQUIRED ON)
+
 add_subdirectory(conversions)
 add_subdirectory(misc)
 add_subdirectory(project_euler)