Basic Language

using System;
using System.Collections.Generic;
using System.Text;

class BasicLanguage
{
  static StringBuilder result = new StringBuilder();

  static void Main()
  {

    bool inBrackets = false;
    StringBuilder buffer = new StringBuilder();

    while (true)
    {
      int nextSymbol = Console.Read();
      if (nextSymbol == -1)
      {
        break;
      }
      char nextChar = (char)nextSymbol;
      if (nextChar =='(')
      {
        inBrackets = true;
      }
      if (nextChar == ')')
      {
        inBrackets = false;
      }
      if (nextChar == ';' && inBrackets == false)
      {
        string statement = buffer.ToString();
        if (ProcessConstruct(statement))
        {
          break;
        }
        buffer.Remove(0, buffer.Length); //buffer clear in .net 4.5
      }
      else
      {
        if (inBrackets)
        {
          buffer.Append(nextChar);
        }
        else if (!char.IsWhiteSpace(nextChar))
        {
          buffer.Append(nextChar);
        }

      }
    }
    Console.WriteLine(result.ToString());
  }

  private static bool ProcessConstruct(string statement)
  {
    string[] commands = statement.Split(')');
    long count = 1;
    for (int i = 0; i < commands.Length; i++)
    {
      string cmd = commands[i];
      cmd = cmd.TrimStart();
      if (cmd.StartsWith("EXIT"))
      {
        return true;
      }
      else if (cmd.StartsWith("PRINT"))
      {
        int start = cmd.IndexOf('(') + 1;
        string content = cmd.Substring(start);
        if (content.Length > 0 && count>0)
        {
          for (int j = 0; j < count; j++)
          {
            result.Append(content);
          }
        }
      }
      else if (cmd.StartsWith("FOR"))
      {
        int startIndex = cmd.IndexOf('(') + 1;
        int commaIndex = cmd.IndexOf(',');
        if (commaIndex == -1)
        {
          string forCountStr = cmd.Substring(startIndex);
          int forCount = int.Parse(forCountStr);
          count *= forCount;
        }
        else
        {
          string forStartCountStr = cmd.Substring(startIndex, commaIndex - startIndex);
          int forStartCount = int.Parse(forStartCountStr);
          string forEndCountStr = cmd.Substring(commaIndex + 1);
          int forEndCount = int.Parse(forEndCountStr);

          int forCount = forEndCount - forStartCount + 1;
          count *= forCount;
        }
      }
    }
    return false;
  }
}