[SoftUni C# exam preparation] Enigmanation

using System;

internal class Enigmanation
{
    private static void Main()
    {
        int symbol = Console.Read();
        decimal sum = 0;
        int o = '+';

        while (symbol != '=')
        {
            if (symbol == '(')
            {
                decimal innerSum = 0;
                int innerO = '+';
                symbol = Console.Read();

                while (symbol != ')')
                {
                    if (0 <= symbol - '0' && symbol - '0' <= 9)
                    {
                        switch (innerO)
                        {
                            case '+':
                                innerSum += symbol - '0';
                                break;

                            case '-':
                                innerSum -= symbol - '0';
                                break;

                            case '*':
                                innerSum *= symbol - '0';
                                break;

                            case '%':
                                innerSum %= symbol - '0';
                                break;
                        }
                    }
                    else if (symbol == '+' ||
                             symbol == '-' ||
                             symbol == '%' ||
                             symbol == '*')
                    {
                        innerO = symbol;
                    }
                    symbol = Console.Read();
                }

                switch (o)
                {
                    case '+':
                        sum += innerSum;
                        break;

                    case '-':
                        sum -= innerSum;
                        break;

                    case '*':
                        sum *= innerSum;
                        break;

                    case '%':
                        sum %= innerSum;
                        break;
                }
            }
            else if (0 <= symbol - '0' && symbol - '0' <= 9)
            {
                switch (o)
                {
                    case '+':
                        sum += symbol - '0';
                        break;

                    case '-':
                        sum -= symbol - '0';
                        break;

                    case '*':
                        sum *= symbol - '0';
                        break;

                    case '%':
                        sum %= symbol - '0';
                        break;
                }
            }
            else if (symbol == '+' ||
                     symbol == '-' ||
                     symbol == '*' ||
                     symbol == '%')
            {
                o = symbol;
            }
            symbol = Console.Read();
        }

        Console.WriteLine("{0:0.000}", sum);
    }
}