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/*
**************************************************************
* C++ Mathematical Expression Toolkit Library *
* *
* Basic Arithmetic Infix Expression Parser And Evaluator *
* 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, T Process(const unsigned char)>
struct char_process : public exprtk::igeneric_function<T>
{
typedef typename exprtk::igeneric_function<T> igfun_t;
typedef typename igfun_t::parameter_list_t parameter_list_t;
typedef typename igfun_t::generic_type generic_type;
typedef typename generic_type::string_view string_t;
using exprtk::igeneric_function<T>::operator();
char_process()
: exprtk::igeneric_function<T>("S")
{}
inline T operator()(parameter_list_t parameters)
{
const unsigned char c = string_t(parameters[0])[0];
return Process(c);
}
};
template <typename T>
T is_digit_func(const unsigned char c)
{
return (('0' <= c) && (c <= '9')) ? T(1) : T(0);
}
template <typename T>
T is_operator_func(const unsigned char c)
{
return ('+' == c) || ('-' == c) ||
('*' == c) || ('/' == c) ;
}
template <typename T>
T to_num_func(const unsigned char c)
{
return static_cast<T>(c - '0');
}
template <typename T>
void basic_arithmetic_parser_evaluator()
{
typedef exprtk::symbol_table<T> symbol_table_t;
typedef exprtk::expression<T> expression_t;
typedef exprtk::parser<T> parser_t;
const std::string arithmetic_parser_evaluator_program =
" var curr_val := 0; "
" var prev_val := 0; "
" var result := 0; "
" var op := '+'; "
" "
" for (var i := 0; i < expression[]; i += 1) "
" { "
" var c := expression[i : i + 1]; "
" "
" if (is_digit(c)) "
" { "
" curr_val := curr_val * 10 + to_num(c); "
" }; "
" "
" if (is_opr(c) or (i == expression[] - 1)) "
" { "
" prev_val := "
" switch "
" { "
" case op == '+' : "
" ~{ "
" result += prev_val; "
" curr_val; "
" }; "
" "
" case op == '-' : "
" ~{ "
" result += prev_val; "
" -curr_val; "
" }; "
" "
" case op == '*' : prev_val * curr_val; "
" case op == '/' : prev_val / curr_val; "
" }; "
" "
" curr_val := 0; "
" op := c; "
" } "
" }; "
" "
" result += prev_val; "
" "
" println(result, ' = ', expression); "
" ";
std::string arithmetic_expression;
char_process<T,is_digit_func<T> > isdigit;
char_process<T,to_num_func<T> > tonum;
char_process<T,is_operator_func<T> > isopr;
exprtk::rtl::io::println<T> println;
symbol_table_t symbol_table;
symbol_table.add_stringvar("expression", arithmetic_expression);
symbol_table.add_function ("println" , println );
symbol_table.add_function ("is_digit" , isdigit );
symbol_table.add_function ("is_opr" , isopr );
symbol_table.add_function ("to_num" , tonum );
expression_t expression;
expression.register_symbol_table(symbol_table);
parser_t parser;
parser.compile(arithmetic_parser_evaluator_program, expression);
/*
Note: Expressions can be comprised of integers,
basic arithmetic operators (+, -, *, /),
and shall not contain parenthesises.
*/
const std::vector<std::string> arithmetic_expressions =
{
"5 + 18 / 3",
"4 + 3 * 15",
"1 - 2 + 52 / 2 - 81 / 3",
};
for (const auto& expr : arithmetic_expressions)
{
arithmetic_expression = expr;
expression.value();
}
}
int main()
{
basic_arithmetic_parser_evaluator<double>();
return 0;
}