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exprtk_simple_example_17.cpp

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exprtk_simple_example_17.cpp

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/*
**************************************************************
* C++ Mathematical Expression Toolkit Library *
* *
* Simple Example 17 *
* 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 <cstdlib>
#include <ctime>
#include <string>
#include "exprtk.hpp"
template <typename T>
struct rnd_01 : public exprtk::ifunction<T>
{
using exprtk::ifunction<T>::operator();
rnd_01() : exprtk::ifunction<T>(0)
{ ::srand(static_cast<unsigned int>(time(NULL))); }
inline T operator()()
{
// Note: Do not use this in production
// Result is in the interval [0,1)
return T(::rand() / T(RAND_MAX + 1.0));
}
};
template <typename T>
void monte_carlo_pi()
{
typedef exprtk::symbol_table<T> symbol_table_t;
typedef exprtk::expression<T> expression_t;
typedef exprtk::parser<T> parser_t;
const std::string monte_carlo_pi_program =
" var samples[2 * 10^8] := [(rnd_01^2 + rnd_01^2) <= 1]; "
" 4 * sum(samples) / samples[]; ";
rnd_01<T> rnd01;
symbol_table_t symbol_table;
symbol_table.add_function("rnd_01",rnd01);
expression_t expression;
expression.register_symbol_table(symbol_table);
parser_t parser;
parser.compile(monte_carlo_pi_program,expression);
const T approximate_pi = expression.value();
const T real_pi = T(3.141592653589793238462643383279502); // or close enough...
printf("pi ~ %20.17f\terror: %20.17f\n",
approximate_pi,
std::abs(real_pi - approximate_pi));
}
int main()
{
monte_carlo_pi<double>();
return 0;
}
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