using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            String str = textBox1.Text;
            String CS = "H";
            label1.Text = "";
            string[] strM = str.Split(' ');
          //  int i = 0;
            int L = strM.Length - 1;
            do
            {
                String c = "";
                for (int i = 0; i <= L; i++)
                {
                    c += strM[i]+ " ";
                }
                label1.Text += c + CS + "=>";

                switch (CS)
                {
                    case ("H"):
                        {
                            if (strM[L] == "e")
                            {
                                CS = "BC";
                            }
                            else
                            {
                                CS = "Error";
                            }
                            break;
                        }
                    case ("BC"):
                        {
                            if (strM[L] == "else" && strM[L - 1] == "e")
                            {
                                L--;
                                CS = "B";
                            }
                            else if (strM[L] == "c")
                            {
                                CS = "A";
                            }
                            else
                            {
                                CS = "Error";
                            }
                            break;
                        }
                    case ("S"):
                        {
                            if (strM[L] == "else" && strM[L - 1] == "e")
                            {
                                L--;
                                CS = "B";
                            }
                            else if (strM[L] == "c")
                            {
                                CS = "A";
                            }
                            else
                            {
                                CS = "Error";
                            }
                            break;
                        }
                    case ("B"):
                        {

                            if (strM[L] == "c")
                            {
                                CS = "A";
                            }
                            else
                            {
                                CS = "Error";
                            }
                            break;
                        }
                    case ("A"):
                        {
                            if(strM[L]=="if")
                            {
                                CS = "S";
                            }
                            else
                            {
                                CS = "Error";
                            }
                            break;
                        }
                }
                L--;
            } while (L !=-1);

            if (CS == "Error")
            {
                MessageBox.Show("Строка не принадлежит грамматике");
            }
            else
            {
                label1.Text += CS;
                MessageBox.Show("Строка принадлежит грамматике");
            }
        }
    }
}