/*

**************************************************************

* C++ Mathematical Expression Toolkit Library *

* *

* Simple Example 04 *

* 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 fibonacci()

{

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;

T x = T(0);

compositor_t compositor;

compositor.add(

function_t("fibonacci")

.var("x")

.expression

(

" switch "

" { "

" case x == 0 : 0; "

" case x == 1 : 1; "

" default : "

" { "

" var prev := 0; "

" var curr := 1; "

" while ((x -= 1) > 0) "

" { "

" var temp := prev; "

" prev := curr; "

" curr += temp; "

" }; "

" }; "

" } "

));

symbol_table_t& symbol_table = compositor.symbol_table();

symbol_table.add_constants();

symbol_table.add_variable("x",x);

std::string expression_str = "fibonacci(x)";

expression_t expression;

expression.register_symbol_table(symbol_table);

parser_t parser;

parser.compile(expression_str,expression);

for (std::size_t i = 0; i < 40; ++i)

{

x = static_cast<T>(i);

const T result = expression.value();

printf("fibonacci(%3d) = %10.0f\n",

static_cast<int>(i),

result);

}

}

int main()

{

fibonacci<double>();

return 0;

}