exprtk_collatz.cpp

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/*
 **************************************************************
 *         C++ Mathematical Expression Toolkit Library        *
 *                                                            *
 * ExprTk Collatz Example                                     *
 * Author: Arash Partow (1999-2025)                           *
 * 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                    *
 * SPDX-License-Identifier: MIT                               *
 *                                                            *
 **************************************************************
*/
 
 
#include <cstdio>
#include <string>
 
#include "exprtk.hpp"
 
 
template <typename T>
void collatz()
{
   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;
 
   exprtk::rtl::io::print<T> print("%3.0f ");
 
   symbol_table_t symbol_table;
   symbol_table.add_function("print",print);
 
   compositor_t compositor(symbol_table);
 
   // define function: collatz_trace(x)
   compositor.add(
      function_t("collatz_trace")
      .var("x")
      .expression
      (
         " while (x > 1)                           "
         " {                                       "
         "    x := (x % 2 == 0) ? x / 2 : 3x + 1;  "
         "    print(x);                            "
         " }                                       "
      ));
 
   const std::string collatz_program =
      " x := 0;              "
      " repeat               "
      "    print(x += 1);    "
      "    collatz_trace(x); "
      "    print('\n\n');    "
      " until (x > 100);     "
      " println;             ";
 
   expression_t expression;
   expression.register_symbol_table(symbol_table);
 
   parser_t parser;
   parser.enable_unknown_symbol_resolver();
   parser.compile(collatz_program,expression);
 
   expression.value();
}
 
int main()
{
   collatz<double>();
   return 0;
}