6 files changed, 104 insertions, 0 deletions
diff --git a/Help/guide/tutorial/Step4/CMakeLists.txt b/Help/guide/tutorial/Step4/CMakeLists.txt
new file mode 100644
index 000000000..38e9b1f72
--- /dev/null
+++ b/Help/guide/tutorial/Step4/CMakeLists.txt
@@ -0,0 +1,32 @@
+cmake_minimum_required(VERSION 3.10)
+
+# set the project name and version
+project(Tutorial VERSION 1.0)
+
+# specify the C++ standard
+set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD_REQUIRED True)
+
+# should we use our own math functions
+option(USE_MYMATH "Use tutorial provided math implementation" ON)
+
+# configure a header file to pass some of the CMake settings
+# to the source code
+configure_file(TutorialConfig.h.in TutorialConfig.h)
+
+# add the MathFunctions library
+if(USE_MYMATH)
+  add_subdirectory(MathFunctions)
+  list(APPEND EXTRA_LIBS MathFunctions)
+endif()
+
+# add the executable
+add_executable(Tutorial tutorial.cxx)
+
+target_link_libraries(Tutorial PUBLIC ${EXTRA_LIBS})
+
+# add the binary tree to the search path for include files
+# so that we will find TutorialConfig.h
+target_include_directories(Tutorial PUBLIC
+                           "${PROJECT_BINARY_DIR}"
+                           )
diff --git a/Help/guide/tutorial/Step4/MathFunctions/CMakeLists.txt b/Help/guide/tutorial/Step4/MathFunctions/CMakeLists.txt
new file mode 100644
index 000000000..0515852a0
--- /dev/null
+++ b/Help/guide/tutorial/Step4/MathFunctions/CMakeLists.txt
@@ -0,0 +1,7 @@
+add_library(MathFunctions mysqrt.cxx)
+
+# state that anybody linking to us needs to include the current source dir
+# to find MathFunctions.h, while we don't.
+target_include_directories(MathFunctions
+          INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
+          )
diff --git a/Help/guide/tutorial/Step4/MathFunctions/MathFunctions.h b/Help/guide/tutorial/Step4/MathFunctions/MathFunctions.h
new file mode 100644
index 000000000..cd36bccff
--- /dev/null
+++ b/Help/guide/tutorial/Step4/MathFunctions/MathFunctions.h
@@ -0,0 +1 @@
+double mysqrt(double x);
diff --git a/Help/guide/tutorial/Step4/MathFunctions/mysqrt.cxx b/Help/guide/tutorial/Step4/MathFunctions/mysqrt.cxx
new file mode 100644
index 000000000..abe767d5a
--- /dev/null
+++ b/Help/guide/tutorial/Step4/MathFunctions/mysqrt.cxx
@@ -0,0 +1,24 @@
+#include <iostream>
+
+#include "MathFunctions.h"
+
+// a hack square root calculation using simple operations
+double mysqrt(double x)
+{
+  if (x <= 0) {
+    return 0;
+  }
+
+  double result = x;
+
+  // do ten iterations
+  for (int i = 0; i < 10; ++i) {
+    if (result <= 0) {
+      result = 0.1;
+    }
+    double delta = x - (result * result);
+    result = result + 0.5 * delta / result;
+    std::cout << "Computing sqrt of " << x << " to be " << result << std::endl;
+  }
+  return result;
+}
diff --git a/Help/guide/tutorial/Step4/TutorialConfig.h.in b/Help/guide/tutorial/Step4/TutorialConfig.h.in
new file mode 100644
index 000000000..e23f5213c
--- /dev/null
+++ b/Help/guide/tutorial/Step4/TutorialConfig.h.in
@@ -0,0 +1,4 @@
+// the configured options and settings for Tutorial
+#define Tutorial_VERSION_MAJOR @Tutorial_VERSION_MAJOR@
+#define Tutorial_VERSION_MINOR @Tutorial_VERSION_MINOR@
+#cmakedefine USE_MYMATH
diff --git a/Help/guide/tutorial/Step4/tutorial.cxx b/Help/guide/tutorial/Step4/tutorial.cxx
new file mode 100644
index 000000000..b3c6a4f43
--- /dev/null
+++ b/Help/guide/tutorial/Step4/tutorial.cxx
@@ -0,0 +1,36 @@
+// A simple program that computes the square root of a number
+#include <cmath>
+#include <iostream>
+#include <string>
+
+#include "TutorialConfig.h"
+
+// should we include the MathFunctions header?
+#ifdef USE_MYMATH
+#  include "MathFunctions.h"
+#endif
+
+int main(int argc, char* argv[])
+{
+  if (argc < 2) {
+    // report version
+    std::cout << argv[0] << " Version " << Tutorial_VERSION_MAJOR << "."
+              << Tutorial_VERSION_MINOR << std::endl;
+    std::cout << "Usage: " << argv[0] << " number" << std::endl;
+    return 1;
+  }
+
+  // convert input to double
+  const double inputValue = std::stod(argv[1]);
+
+  // which square root function should we use?
+#ifdef USE_MYMATH
+  const double outputValue = mysqrt(inputValue);
+#else
+  const double outputValue = sqrt(inputValue);
+#endif
+
+  std::cout << "The square root of " << inputValue << " is " << outputValue
+            << std::endl;
+  return 0;
+}