evalExp.C

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
 
# include <cctype>
# include <cstring>
# include <cstdlib>
# include <iostream>
# include <tclap/CmdLine.h>
# include <tpl_arrayStack.H>
 
using namespace std;
using namespace Aleph;
 
enum Token_Type { Value, Operator, Lpar, Rpar, End, Error };
 
Token_Type lexer(char *& str, size_t & len)
{
  str += len;
  len = 1;
  
  while (isblank(*str))
    str++;
    
  switch (*str)
    {
    case '(':  return Lpar;
    case ')':  return Rpar;
    case '+':
    case '-':
    case '*':
    case '/':  return Operator;
    case '\0': return End;
    }
    
  if (not isdigit(*str)) 
    return Error;
    
  char* base = str + 1;
  while (isdigit(*base++))
    len++;
    
  return Value;
}
 
char * str_to_token(const char * token_str, const size_t & len)
{
  static char buffer[256];
  strncpy(buffer, token_str, len); 
  buffer[len] = '\0';
  return buffer;
}
 
unsigned precedence(const char & op)
{
  switch (op)
    {
    case '$': return 0;  // Stack bottom marker
    case '(': return 1;
    case '+':
    case '-': return 2;
    case '/':
    case '*': return 3;
    default: 
      cerr << "Invalid operator: " << op << endl;
      exit(1);
    }
}
 
void apply(ArrayStack<int>& val_stack, ArrayStack<char>& op_stack)
{
  if (op_stack.size() == 0)
    {
      cerr << "Error: operator stack empty" << endl;
      exit(1);
    }
  if (val_stack.size() < 2)
    {
      cerr << "Error: not enough operands" << endl;
      exit(1);
    }
 
  const char the_operator = op_stack.pop(); 
  const int right_operand = val_stack.pop();
  const int left_operand  = val_stack.pop();
  int result;
  
  switch (the_operator)
    {
    case '+': result = left_operand + right_operand; break;
    case '-': result = left_operand - right_operand; break;
    case '*': result = left_operand * right_operand; break;
    case '/': 
      if (right_operand == 0)
        {
          cerr << "Error: division by zero" << endl;
          exit(1);
        }
      result = left_operand / right_operand; 
      break;
    default: 
      cerr << "Invalid operator: " << the_operator << endl;
      exit(1);
    }
    
  val_stack.push(result);
}
 
int eval(char* input)
{
  ArrayStack<int>  val_stack;
  ArrayStack<char> op_stack;
  size_t token_len = 0;
  
  op_stack.push('$');  // Stack bottom marker
  
  while (true)
    {
      switch (lexer(input, token_len))
        {
        case Value:
          {
            const int operand = atoi(str_to_token(input, token_len));
            val_stack.push(operand);
            break;
          }
          
        case Lpar: 
          op_stack.push(*input);
          break;
          
        case Operator: 
          while (precedence(op_stack.top()) >= precedence(*input))
            apply(val_stack, op_stack);
          op_stack.push(*input);
          break;
          
        case Rpar: 
          while (op_stack.top() != '(')
            {
              if (op_stack.top() == '$')
                {
                  cerr << "Error: mismatched parentheses" << endl;
                  exit(1);
                }
              apply(val_stack, op_stack);
            }
          op_stack.pop();  // Remove the '('
          break;
          
        case End:
          while (op_stack.top() != '$')
            apply(val_stack, op_stack);
          op_stack.pop();  // Remove '$'
          
          if (val_stack.size() != 1 or op_stack.size() != 0)
            {
              cerr << "Error: malformed expression" << endl;
              exit(1);
            }
          return val_stack.pop();
 
        case Error:
        default: 
          cerr << "Error: invalid token at position" << endl;
          exit(1);
        } 
    }
}
 
int main(int argc, char** argv)
{
  try
    {
      TCLAP::CmdLine cmd("Arithmetic expression evaluator", ' ', "1.0");
 
      TCLAP::UnlabeledValueArg<string> exprArg("expression",
                                                "Arithmetic expression to evaluate (use quotes)",
                                                true, "", "expression");
      cmd.add(exprArg);
 
      cmd.parse(argc, argv);
 
      string expr = exprArg.getValue();
      
      cout << "Expression Evaluator" << endl;
      cout << "====================" << endl;
      cout << "Input: " << expr << endl;
      
      // Create mutable copy for lexer
      char* input = new char[expr.size() + 1];
      strcpy(input, expr.c_str());
      
      int result = eval(input);
      
      cout << "Result: " << result << endl;
      
      delete[] input;
    }
  catch (TCLAP::ArgException &e)
    {
      cerr << "Error: " << e.error() << " for arg " << e.argId() << endl;
      return 1;
    }
 
  return 0;
}