C++ Reverse Polish Notation calulator

.gitignore

.vs/RPN/v14/.suo
Debug/RPN.exe
Debug/RPN.log
Debug/RPN.pdb
Debug/RPN.tlog/CL.command.1.tlog
Debug/RPN.tlog/CL.read.1.tlog
Debug/RPN.tlog/CL.write.1.tlog
*.tlog
*.ilk
*.idb
Debug/vc140.pdb
*.obj
RPN.VC.db
RPN.VC.VC.opendb
RPN.vcxproj.filters
*.exe
*.pdb
*.log

rpn.cpp

// Reverse Polish notation demo
// Basic calulator for RPN expression only + / * - is supported.
// Allows ints and floats.

// By DreamVB (dreamvb@outlook.com) 20:08 26/09/2016
// Forked by Tom240965 https://gist.github.com/Tom240965/47002094487f40297af5b69715457a24

#include <iostream>
#include <string>
#include <stack>
#include <stdexcept>

namespace Ben
{
  #define MAX_STACK 100
  float _stack[MAX_STACK];
  int tos = 0;
  
  bool Full(){
  	return tos >= MAX_STACK - 1;
  }
  
  bool Empty(){
  	return tos == 0;
  }
  
  void Push(float value){
  	if (Full()){
  		return;
  	}
  	tos++;
  	_stack[tos] = value;
  }
  
  float Pop(){
  	float t = _stack[tos];
  	tos--;
  	return t;
  }
  bool IsOp(char c)
  {
    //Check for operators.
    switch (c)
    {
      case '+':
      case '-':
      case '*':
      case '/':
        return true;
      default:
        return false;
    }
  }

  double RPN(const std::string& expression)
  {
    size_t i = 0;
    float v1, v2, ret;
    v1 = ret = v2 = 0.0;

    std::string tok;

    while (i < expression.length()) {
      //Skip white space
      while (isspace(expression[i])) {
        i++;
      }
      //Check for digits and .
      if (isdigit(expression[i]) || expression[i] == '.') 
      {
        while (isdigit(expression[i]) || expression[i] == '.') 
        {
          tok += expression[i];
          i++;
        }
        //Push on stack number.
        Push((float)atof(tok.c_str()));
        tok = "";
      }
      //Check for operator
      else if (IsOp(expression[i])) {
        if (expression[i] == '+') {
          v1 = Pop();
          v2 = Pop();
          ret = (v1 + v2);
        }
        if (expression[i] == '-') {
          v1 = Pop();
          v2 = Pop();
          ret = v2 - v1;
        }
        if (expression[i] == '*') {
          v1 = Pop();
          v2 = Pop();
          ret = (v1 * v2);
        }
        if (expression[i] == '/') {
          v1 = Pop();
          v2 = Pop();
          ret = (v2 / v1);
        }
        //INC Counter
        i++;
        //Push result onto stack
        Push(ret);
      }
      else 
        throw std::runtime_error("Invaild Expression.");
        
    }
    //Return answer
    return Pop();
  }
}

namespace Tom
{
  double RPN(const std::string& expression)
  {
    std::stack<float> numbers;
    size_t i = 0;
    float v1, v2, ret;
    v1 = ret = v2 = 0.0;

    std::string tok;

    while (i < expression.length())
    {
      //Skip white space
      while (isspace(expression[i]))
      {
        i++;
      }
      //Check for digits and .
      if (isdigit(expression[i]) || expression[i] == '.')
      {
        while (isdigit(expression[i]) || expression[i] == '.')
        {
          tok += expression[i];
          i++;
        }
        //Push on stack number.
        //Push(atof(tok.c_str()));
        numbers.push((float)atof(tok.c_str()));
        tok = "";
      }
      //Check for operator
      else if (Ben::IsOp(expression[i]))
      {
        if (expression[i] == '+')
        {
          if (numbers.size() < 2)
            throw std::runtime_error("Error in expression - not 2 numbers in stack");
          v1 = numbers.top();
          numbers.pop();
          v2 = numbers.top();
          numbers.pop(); 
          ret = (v1 + v2);
        }
        if (expression[i] == '-') 
        {
          if (numbers.size() < 2)
            throw std::runtime_error("Error in expression - not 2 numbers in stack");
          v1 = numbers.top();
          numbers.pop();
          v2 = numbers.top();
          numbers.pop();
          ret = v2 - v1;
        }
        if (expression[i] == '*') 
        {
          if (numbers.size() < 2)
            throw std::runtime_error("Error in expression - not 2 numbers in stack");
          v1 = numbers.top();
          numbers.pop();
          v2 = numbers.top();
          numbers.pop();
          ret = (v1 * v2);
        }
        if (expression[i] == '/') 
        {
          if (numbers.size() < 2)
            throw std::runtime_error("Error in expression - not 2 numbers in stack");
          v1 = numbers.top();
          numbers.pop();
          v2 = numbers.top();
          numbers.pop();
          ret = (v2 / v1);
        }
        //INC Counter
        i++;
        //Push result onto stack
        numbers.push(ret);
      }
      else 
      {
        std::cout << "Invaild Expression." << std::endl;
        break;
      }
    }
    //Return answer
    if (numbers.size() != 1)
      throw std::runtime_error("Stack doesn't contain result");
    
    return numbers.top();
  }
}


int main()
{
  using std::cout;
  using std::endl;

  try
  {
    system("title RPN Calulator Demo");
    //Infix == (4 * (12 + 3) / 2 * (5 + 5) - (100 * 2))/2 Answer 50
    std::string expr = "4 12 3 + * 2 / 5 5 + * 100 2 * - 2 /";

    cout << "Expression  : " << expr.c_str() << endl;
    cout << "Answer      : " << Tom::RPN(expr) << endl << endl;
    cout << "Expression  : " << "22 7 /" << endl;
    cout << "PI          : " << Tom::RPN("22 7 /") << endl;

    system("pause");
  }
  catch (const std::exception& ex)
  {
    std::cerr << "Error: " << ex.what() << "\n\n";
    return 1;
  }
  #ifdef _DEBUG
    system("pause");
  #endif
  // return 0; not needed since default
}

RPN.sln


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