using System;

using System.Collections.Generic;

using System.IO;

using System.Linq;

using System.Text;

using System.Text.RegularExpressions;

using System.Threading.Tasks;

public static class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        string myString = "5/5 + 5 *-5 - 5*5 + 27"; // BAD "5/-5 + 5 *5 - 5*5 + 27";   // BAD2: "5/5 + 5 *5 - 5*5 + 27"

        myString = "1/2 + 3 *-4 - 5*6 + 7"; 

        myString = myString.RemoveWhitespace();

        string result = RecursiveEvaluate(myString);

        Console.WriteLine("result:" + result);

    }

            public static string[] Operators = { "*", "/", "+", "-" };

        public static string RecursiveEvaluate(string lineRaw)

        {

            string[] elements_LB;

            int LEVEL;

            string op;

            Regex regex;

            for (int i = 0; i < Operators.Length; i++) // go over all operators in order BODMAS

            {      

                op = Operators[i]; // split by an operator, eg "*" 

                elements_LB = lineRaw.Split(op);  // 3 + 5*3 -1   --> 3+5,  3-1

                LEVEL = 0;

                while (elements_LB.Length > 1) // keep going until we haven't yet evaluated all for this type of operator

                {

                    LEVEL++;

                    Console.WriteLine("PROCESSING lineRaw: " +lineRaw+ " / with op'" + op + "' operator LEVEL " + LEVEL);

                   // if (elements_LB.Length == 1) continue; // if finished with this type of operator

                    //DebugSoFar(elements_LB);

                    int firstIndex = FindFirstIndex(elements_LB);

​

                    // get what is immediately before, and after the first occurrence of this operator

                    string leftSide = elements_LB[firstIndex];  // 3+5

                    string rightSide = elements_LB[firstIndex+1]; // 3-1

Console.WriteLine("leftSide: " +leftSide+ " / rightSide:" + rightSide);

                    // split by both sides by ANY of the operators, to be able to extract the actual terms to be multiplied together

                   // string[] leftSideSplit = leftSide.Split(Operators, StringSplitOptions.None); // 3, 5

                   // string[] rightSideSplit = rightSide.Split(Operators, StringSplitOptions.None); // 3, -1

​

                    string left = GetLastElementOnLeft(leftSide);// 5 (grab the last)

                    string right = GetFirstElementOnRight(rightSide);// 3 (grab the first)

                   // string left = leftSideSplit[leftSideSplit.Length - 1];// 5 (grab the last)

                   // string right = rightSideSplit[0];// 3 (grab the first)

Console.WriteLine("left: " +left+ " / right:" + right);

                    // perform calculation

                    string result = op.Operator(int.Parse(left), int.Parse(right)).ToString();// 5 * 3 = 8

​

                    // regenerate the string for next iteration:

                    // replace the bit that we have just evaluated in the original string, with what we have evaluated it into:

                    regex = new Regex(Regex.Escape(left + op + right)); // 5*3

                    lineRaw = regex.Replace(lineRaw, result, 1); // 3 + 5*3 -1 -> 3 + 15 -1

                    elements_LB = lineRaw.Split(op);  // perform split again

                }

            }

​

            return lineRaw;

        }

            private static string GetLastElementOnLeft(string leftSide) // 5 -3

        {

            int counter = 0;

            for (int i = leftSide.Length-1; i >= 0  ; i--)

            {

                //Console.WriteLine(leftSide + " / leftSide[i]: " + leftSide[i]);

                // if it is -5 * 3, then we do NOT want to return just the minus sign

                // if (i == 0 && rightSide[i].ToString() == "-") continue;

​

                if (Array.IndexOf(Operators, leftSide[i].ToString()) != -1)

                {

                    string returnString = leftSide.Substring(i+1, counter); // get it from the previous iteration

                    if ( i > 0 ) // only if we haven't run out of the string

                    {

                        // if the previous character would have been a minus sign, then we must also add that

                        if (leftSide[i].ToString() == "-") returnString+= "-" + returnString;

                        Console.WriteLine(leftSide + " / leftSide[i]: "  + leftSide[i]);

​

                    }

                    Console.WriteLine("returnString: "  + returnString);

                    return returnString;

                }

                counter++;

            }

            return leftSide;

        }

​

​

        private static string GetFirstElementOnRight(string rightSide)

        {

            for (int i = 0; i < rightSide.Length; i++)

            {

                // if it is -5 * 3, then we do NOT want to return just the minus sign

                if (i == 0 && rightSide[i].ToString() == "-") continue;

​

                if (Array.IndexOf(Operators, rightSide[i].ToString()) != -1)

                    return rightSide.Substring(0, i );

​

            }

            return rightSide;

        }

​

​

​

        public static int Operator(this string op, int x, int y)

        {

            switch (op)

            {

                case "*": return x * y;

                case "/": return x / y;

                case "+": return x + y;

                case "-": return x - y;

                default: throw new Exception("invalid logic");

            }

        }

      private static void DebugSoFar(string[] words)

        {

            Console.WriteLine("split result length: " + words.Length);

            for (int i = 0; i < words.Length; i++)

                Console.WriteLine(words[i] + ", ");

        }

​

​

        private static int FindFirstIndex(string[] words)

        {

            for (int i = 0; i < words.Length; i++)

                if (words[i] != "") return i;

​

            return -1;

        }

​

        private static int FindLastIndex(string[] words)

        {

            int lastInstance = -1;

            for (int i = 0; i < words.Length; i++)

                if (words[i] != "") lastInstance = i;

​

            return lastInstance;

        }

​

​

​

        public static string RemoveWhitespace(this string input)

        {

            return new string(input.ToCharArray()

                .Where(c => !Char.IsWhiteSpace(c))

                .ToArray());

        }

​

        /// <summary>

        /// Gets the key value separator.

        /// </summary>

        /// <value>

        /// The key value separator.

        /// </value>

        public static string KeyValueSeparator = "=";

​

        /// <summary>

        /// Gets the comment characters.

        /// </summary>

        /// <value>

        /// The comment characters.

        /// </value>

        public static string[] CommentCharacters = { "#", ";", "//" };

​

​

}