exprtk_simple_example_11.cpp

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/*
 **************************************************************
 *         C++ Mathematical Expression Toolkit Library        *
 *                                                            *
 * Simple Example 11                                          *
 * Author: Arash Partow (1999-2024)                           *
 * 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 square_wave2()
{
   typedef exprtk::symbol_table<T> symbol_table_t;
   typedef exprtk::expression<T>   expression_t;
   typedef exprtk::parser<T>       parser_t;
 
   const std::string wave_program =
      " var r := 0;                                          "
      "                                                      "
      " for (var i := 0; i < 1000; i += 1)                   "
      " {                                                    "
      "    r += (1 / (2i + 1)) * sin((4i + 2) * pi * f * t); "
      " };                                                   "
      "                                                      "
      " r *= a * (4 / pi);                                   ";
 
   static const T pi = T(3.141592653589793238462643383279502);
 
   T f = pi / T(10);
   T t = T(0);
   T a = T(10);
 
   symbol_table_t symbol_table;
   symbol_table.add_variable("f",f);
   symbol_table.add_variable("t",t);
   symbol_table.add_variable("a",a);
   symbol_table.add_constants();
 
   expression_t expression;
   expression.register_symbol_table(symbol_table);
 
   parser_t parser;
   parser.compile(wave_program,expression);
 
   const T delta = (T(4) * pi) / T(1000);
 
   for (t = (T(-2) * pi); t <= (T(+2) * pi); t += delta)
   {
      const T result = expression.value();
      printf("%19.15f\t%19.15f\n", t, result);
   }
}
 
int main()
{
   square_wave2<double>();
   return 0;
}