Exercise07Expression ver 2

/*Write a program that calculates the value of given arithmetical expression. The expression can contain the following elements only:
*Real numbers, e.g. 5, 18.33, 3.14159, 12.6
*Arithmetic operators: +, -, *, / (standard priorities)
*Mathematical functions: ln(x), sqrt(x), pow(x,y)
*Brackets (for changing the default priorities)
*Examples:
*(3+5.3) * 2.7 - ln(22) / pow(2.2, -1.7) ---> ~ 10.6
*pow(2, 3.14) * (3 - (3 * sqrt(2) - 3.2) + 1.5*0.3) ---> ~ 21.22
*Hint: Use the classical "shunting yard" algorithm and "reverse Polish notation".*/

using System;
using System.Globalization;
using System.Text;
using System.Threading;

public class Exercise07Expression
{
    private static void Main()
    {
        Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
        Console.Write("\nPlease enter expression like this (3+5.3) * 2.7 - ln(22) / pow(2.2, -1.7) : ");
        string test = Console.ReadLine();
        StringBuilder expression = new StringBuilder();
        expression.Append('(', 2);
        foreach (var item in test)
        {
            if (item != ' ')
            {
                expression.Append(item);
            }
        }

        expression.Append(')', 2);

        while (SearchBrackets(expression) != 0)
        {
            expression = CalculateExpression(true, SearchBrackets(expression), expression);
        }

        Console.WriteLine("\n\nResult is: {0}\n\n", expression);
    }

    private static decimal ExtractNum(int offset, int startPoint, StringBuilder expression)
    {
        int temp = 0;
        StringBuilder result = new StringBuilder();
        startPoint += offset;
        if (offset > 0 && (expression[startPoint] == '-' || expression[startPoint] == '+'))
        {
            result.Append(expression[startPoint]);
            startPoint += offset;
        }

        while (int.TryParse(expression[startPoint].ToString(), out temp) || expression[startPoint] == '.')
        {
            if (offset == -1)
            {
                result.Insert(0, expression[startPoint]);
                if ((expression[startPoint - 1] == '-' || expression[startPoint - 1] == '+') && !int.TryParse(expression[startPoint - 2].ToString(), out temp))
                {
                    result.Insert(0, expression[startPoint - 1]);
                }
            }
            else
            {
                result.Append(expression[startPoint]);
            }

            if (startPoint > 0 && startPoint < expression.Length - 1)
            {
                startPoint += offset;
            }
            else
            {
                break;
            }
        }

        return decimal.Parse(result.ToString());
    }

    private static StringBuilder Calculate(int startPoint, StringBuilder expression)
    {
        decimal result = 0;
        switch (expression[startPoint])
        {
            case '-':
                {
                    result = ExtractNum(-1, startPoint, expression) - ExtractNum(1, startPoint, expression);
                    return Exchange(startPoint - ExtractNum(-1, startPoint, expression).ToString().Length, startPoint + ExtractNum(1, startPoint, expression).ToString().Length + 1, result.ToString(), expression);
                }

            case '+':
                {
                    result = ExtractNum(-1, startPoint, expression) + ExtractNum(1, startPoint, expression);
                    return Exchange(startPoint - ExtractNum(-1, startPoint, expression).ToString().Length, startPoint + ExtractNum(1, startPoint, expression).ToString().Length + 1, result.ToString(), expression);
                }

            case '*':
                {
                    result = ExtractNum(-1, startPoint, expression) * ExtractNum(1, startPoint, expression);
                    return Exchange(startPoint - ExtractNum(-1, startPoint, expression).ToString().Length, startPoint + ExtractNum(1, startPoint, expression).ToString().Length + 1, result.ToString(), expression);
                }

            default:
                {
                    result = ExtractNum(-1, startPoint, expression) / ExtractNum(1, startPoint, expression);
                    return Exchange(startPoint - ExtractNum(-1, startPoint, expression).ToString().Length, startPoint + ExtractNum(1, startPoint, expression).ToString().Length + 1, result.ToString(), expression);
                }
        }
    }

    private static StringBuilder Exchange(int startIndex, int endIndex, string valueToExchange, StringBuilder expression)
    {
        expression.Remove(startIndex, endIndex - startIndex);
        expression.Insert(startIndex, valueToExchange);
        return expression;
    }

    private static StringBuilder CalculateFunc(int startIndex, StringBuilder expression)
    {
        CalculateExpression(false, startIndex, expression);
        decimal result = 0;
        switch (expression[startIndex - 1])
        {
            case 'n':
                {
                    result = (decimal)Math.Log((double)ExtractNum(1, startIndex, expression));
                    return Exchange(startIndex - 2, startIndex + ExtractNum(1, startIndex, expression).ToString().Length + 2, result.ToString(), expression);
                }

            case 't':
                {
                    result = (decimal)Math.Sqrt((double)ExtractNum(1, startIndex, expression));
                    return Exchange(startIndex - 4, startIndex + ExtractNum(1, startIndex, expression).ToString().Length + 2, result.ToString(), expression);
                }

            default:
                {
                    int startIndex2 = startIndex;
                    while (expression[startIndex2] != ',')
                    {
                        startIndex2++;
                    }

                    result = (decimal)Math.Pow((double)ExtractNum(-1, startIndex2, expression), (double)ExtractNum(1, startIndex2, expression));
                    return Exchange(startIndex - 3, startIndex + ExtractNum(-1, startIndex2, expression).ToString().Length + ExtractNum(1, startIndex2, expression).ToString().Length + 3, result.ToString(), expression);
                }
        }
    }

    private static int SearchBrackets(StringBuilder expression)
    {
        int index = 0;
        int result = 0;
        while (index < expression.Length && expression[index] != ')')
        {
            if (expression[index] == '(')
            {
                result = index;
            }

            index++;
        }

        return result;
    }

    private static StringBuilder CalculateExpression(bool checkForFunc, int startIndex, StringBuilder expression)
    {
        if (checkForFunc)
        {
            int mod = 1;
            if (startIndex == 0)
            {
                mod = 0;
            }

            if (expression[startIndex - mod] == 'n' || expression[startIndex - mod] == 't' || expression[startIndex - mod] == 'w')
            {
                return CalculateFunc(startIndex, expression);
            }
        }

        while (SearchSign('*', startIndex, expression) != 0)
        {
            expression = Calculate(SearchSign('*', startIndex, expression), expression);
        }

        while (SearchSign('/', startIndex, expression) != 0)
        {
            expression = Calculate(SearchSign('/', startIndex, expression), expression);
        }

        while (SearchSign('-', startIndex, expression) != 0 || SearchSign('+', startIndex, expression) != 0)
        {
            while (SearchSign('+', startIndex, expression) != 0)
            {
                if (SearchSign('-', startIndex, expression) != 0 && (SearchSign('-', startIndex, expression) < SearchSign('+', startIndex, expression)))
                {
                    break;
                }

                expression = Calculate(SearchSign('+', startIndex, expression), expression);
            }

            while (SearchSign('-', startIndex, expression) != 0)
            {
                expression = Calculate(SearchSign('-', startIndex, expression), expression);
            }
        }

        if (checkForFunc)
        {
            expression.Remove(startIndex, 1);
            while (expression[startIndex] != ')')
            {
                startIndex++;
            }

            expression.Remove(startIndex, 1);
        }

        return expression;
    }

    private static int SearchSign(char sign, int startIndex, StringBuilder expression)
    {
        int resultIndex = 0;
        while (expression[startIndex] != ')' && startIndex < expression.Length)
        {
            bool check = expression[startIndex - 1] == '*' || expression[startIndex - 1] == '/' || expression[startIndex - 1] == '+' || expression[startIndex - 1] == '-' || expression[startIndex - 1] == ',' || expression[startIndex - 1] == '(';
            if (expression[startIndex] == sign &&  !check)
            {
                resultIndex = startIndex;
                break;
            }

            startIndex++;
        }

        return resultIndex;
    }
}