Add ExprTk_BUILD_EXAMPLES to build examples

Also move examples into an examples folder

examples/exprtk_simple_example_03.cpp

@@ -0,0 +1,59 @@
+/*
+ **************************************************************
+ *         C++ Mathematical Expression Toolkit Library        *
+ *                                                            *
+ * Simple Example 3                                           *
+ * 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 polynomial()
+{
+   typedef exprtk::symbol_table<T> symbol_table_t;
+   typedef exprtk::expression<T>   expression_t;
+   typedef exprtk::parser<T>       parser_t;
+
+   const std::string expression_string =
+                  "25x^5 - 35x^4 - 15x^3 + 40x^2 - 15x + 1";
+
+   const T r0 = T(0);
+   const T r1 = T(1);
+         T  x = T(0);
+
+   symbol_table_t symbol_table;
+   symbol_table.add_variable("x",x);
+
+   expression_t expression;
+   expression.register_symbol_table(symbol_table);
+
+   parser_t parser;
+   parser.compile(expression_string,expression);
+
+   const T delta = T(1.0 / 100.0);
+
+   for (x = r0; x <= r1; x += delta)
+   {
+      printf("%19.15f\t%19.15f\n", x, expression.value());
+   }
+}
+
+int main()
+{
+   polynomial<double>();
+   return 0;
+}