Add ExprTk_BUILD_EXAMPLES to build examples

Also move examples into an examples folder

examples/exprtk_simple_example_01.cpp

@@ -0,0 +1,57 @@
+/*
+ **************************************************************
+ *         C++ Mathematical Expression Toolkit Library        *
+ *                                                            *
+ * Simple Example 1                                           *
+ * 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 trig_function()
+{
+   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 =
+                     "clamp(-1.0,sin(2 * pi * x) + cos(x / 2 * pi),+1.0)";
+
+   T x;
+
+   symbol_table_t symbol_table;
+   symbol_table.add_variable("x",x);
+   symbol_table.add_constants();
+
+   expression_t expression;
+   expression.register_symbol_table(symbol_table);
+
+   parser_t parser;
+   parser.compile(expression_string,expression);
+
+   for (x = T(-5); x <= T(+5); x += T(0.001))
+   {
+      const T y = expression.value();
+      printf("%19.15f\t%19.15f\n", x, y);
+   }
+}
+
+int main()
+{
+   trig_function<double>();
+   return 0;
+}