Add ExprTk_BUILD_EXAMPLES to build examples

Also move examples into an examples folder

examples/exprtk_simple_example_04.cpp

@@ -0,0 +1,87 @@
+/*
+ **************************************************************
+ *         C++ Mathematical Expression Toolkit Library        *
+ *                                                            *
+ * Simple Example 4                                           *
+ * Author: Arash Partow (1999-2023)                           *
+ * URL: https://www.partow.net/programming/exprtk/index.html  *
+ *                                                            *
+ * Copyright notice:                                          *
+ * Free use of the Mathematical Expression Toolkit Library is *
+ * permitted under the guidelines and in accordance with the  *
+ * most current version of the MIT License.                   *
+ * https://www.opensource.org/licenses/MIT                    *
+ *                                                            *
+ **************************************************************
+*/
+
+
+#include <cstdio>
+#include <string>
+
+#include "exprtk.hpp"
+
+template <typename T>
+void fibonacci()
+{
+   typedef exprtk::symbol_table<T>         symbol_table_t;
+   typedef exprtk::expression<T>           expression_t;
+   typedef exprtk::parser<T>               parser_t;
+   typedef exprtk::function_compositor<T>  compositor_t;
+   typedef typename compositor_t::function function_t;
+
+   compositor_t compositor;
+
+   compositor
+      .add(
+      function_t( // define function: fibonacci(x)
+           "fibonacci",
+           " var w := 0;             "
+           " var y := 0;             "
+           " var z := 1;             "
+           " switch                  "
+           " {                       "
+           "   case x == 0 : 0;      "
+           "   case x == 1 : 1;      "
+           "   default     :         "
+           "    while ((x -= 1) > 0) "
+           "    {                    "
+           "      w := z;            "
+           "      z := z + y;        "
+           "      y := w;            "
+           "      z                  "
+           "    };                   "
+           " }                       ",
+           "x"));
+
+   T x = T(0);
+
+   symbol_table_t& symbol_table = compositor.symbol_table();
+   symbol_table.add_constants();
+   symbol_table.add_variable("x",x);
+
+   std::string expression_str = "fibonacci(x)";
+
+   expression_t expression;
+   expression.register_symbol_table(symbol_table);
+
+   parser_t parser;
+   parser.compile(expression_str,expression);
+
+   for (std::size_t i = 0; i < 40; ++i)
+   {
+      x = static_cast<T>(i);
+
+      const T result = expression.value();
+
+      printf("fibonacci(%3d) = %10.0f\n",
+             static_cast<int>(i),
+             result);
+   }
+}
+
+int main()
+{
+   fibonacci<double>();
+   return 0;
+}