C#

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

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

private void button1_Click(object sender, EventArgs e)
{
int countx1 = 0, countx2 = 0, i = 0, x = 0, y = 0, letterctr = 0;
char[] pew = textBox1.Text.ToCharArray();
int len = pew.Length;

while (i < len)
{
if(pew[i].Equals('x')||pew[i].Equals('y'))
letterctr++;
i++;
}
if(letterctr==0)
{
MessageBox.Show("Valid");
}
else if(letterctr == len){
if(pew[0].Equals('x')){
while(pew[x].Equals('x')){
if(x==len)break;
countx1++; x++;
}
Array.Reverse(pew);
while(pew[y].Equals('x')){
countx2++;
y++;
}
if(countx1==countx2){
MessageBox.Show("Valid");
}
else
MessageBox.Show("Invalid");

}
else
MessageBox.Show("Invalid");
}
else
MessageBox.Show("Invalid");
}
}
}