Infix for Postfix and Unary / Binary Operators

Question

I have a piece of code that converts an infix expression into an expression tree in memory. It works great. There is only one small problem. I just bind how to use unary operators (right associative) correctly.

With the following infix expression:

+1 + +2 - -3 - -4

I would expect an RPN:

1+2++3-4--

However, none of the infix-post online converters I can find this example as I expected. Does anyone have a clear explanation of handling the correct associative operators, in particular binary ones, which can be taken as unary?

Edit / Explanation: I would like to know how to handle unary operators when translating from infix to postfix. That is: recognition of the same "-" character, for example, as a unary, not a binary operator and, therefore, a different priority. I would think about using a state machine, perhaps with two states, but ...?

Answer 1

Well, you need to determine if a given operator is binary / unary during the parsing step. When you do this, when creating an RPN, you can mark the statements as taking 2 or 1 arguments.

Shunting Yard ( RPN ), .

, , , - + -, 0 , + -, "".

+1 + +2 - -3 - -4

(0+1) + (0+2) - (0-3) - (0-4)

+ - , , , .

Answer 2

, # . , . , ​​ , false . , PFE. '#' '~' (PFE).

, 1 + -1,1 + (- 1), 1 --- 1,1 + - 1, .

using System;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace DSA
{
    class Calculator
    {
        string PFE;
        public Calculator()
        {
            Console.WriteLine("Intializing Calculator");
        }

        public double Calculate(string expression)
        {
            ConvertToPost(expression);
            return CalculatePOST();
        }

        public void ConvertToPost(string expression)
        {
            expression = "(" + expression + ")";

            var temp = new DSA.Stack<char>();
            string ch = string.Empty;
            bool unary = true;
            char a;
            foreach (var b in expression)
            {
                a = b;
                if (!a.IsOperator()) {
                    ch += a.ToString();
                    unary = false;
                }
                else
                {
                    if (ch!=string.Empty) 
                    PFE += ch+",";
                    ch = string.Empty;
                    if(a!='(' && a!=')')
                    {
                        if (unary == true)
                        {
                            if (a == '-') a = '~'; else if (a == '+') a = '#'; else throw new InvalidOperationException("invalid input string");
                        }
                        try
                        {
                            if (a.Precedence() <= temp.Peek().Precedence())
                            {
                                PFE += temp.Pop().ToString() + ",";
                            }
                          }
                        catch(InvalidOperationException e)
                        {

                        }

                            temp.Push(a);
                            unary = true;
                    }
                    if (a == '(') { temp.Push(a);}
                    if(a==')')
                    {
                       for(char t=temp.Pop();t!='(';t=temp.Pop())
                        {
                            PFE += t.ToString() + ","; 
                        }
                    }
                }

            }

        }

        public double CalculatePOST()
        {
            var eval = new Stack<double>();
            string ch = string.Empty;
            bool skip = false;
            foreach(char c in PFE)
            {
                if(!c.IsOperator())
                {
                    if (c == ',')
                    {
                        if (skip == true)

                        {
                            skip = false;
                            continue;
                        }
                        eval.Push(Double.Parse(ch));
                        ch = string.Empty;
                    }
                    else ch += c;
                }
                else
                {
                    if (c == '~')
                    {
                        var op1 = eval.Pop();
                        eval.Push(-op1);
                    }
                    else if (c == '#') ;
                    else
                    {
                        var op2 = eval.Pop();
                        var op1 = eval.Pop();
                        eval.Push(Calc(op1, op2, c));
                    }
                    skip = true;
                }
              }
            return eval.Pop();
        }

        private double Calc(double op1, double op2, char c)
        {   
           switch(c)
            {

                case '+':
                    return op1 + op2;
                case '-':
                    return op1 - op2;
                case '*':
                    return op1 * op2;
                case '%':
                    return op1 % op2;
                case '/':
                    return op1 / op2;
                case '^':
                    return float.Parse(Math.Pow(op1,op2).ToString());
                default:
                    throw new InvalidOperationException();
            }
        }
    }


    public static class extension
    {
        public static bool IsOperator(this char a)
        {
            char[] op = {'+','-','/','*','(',')','^','!','%','~','#'};
             return op.Contains(a);
        }

        public static int Precedence(this char a)
        {
            if (a == '~' || a== '#')
                return 1;
            if (a == '^')
                return 0;
            if (a == '*' || a == '/' || a=='%')
                return -1;
            if (a == '+' || a == '-')
                return -2;
            return -3;       
        }       
    }
}