Not able to increment the values of the database

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;
using System.Data.SqlClient;

namespace online_test
{
    public partial class Form1 : Form
    {
        int incre = 0;
        public Form1()
        {
            InitializeComponent();
            radioButton1.TabStop = false;
            radioButton2.TabStop = false;
            radioButton3.TabStop = false;
            radioButton4.TabStop = false;
            //qn1();
            
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //string source_1 = @"DataSource=(LocalDB)\MSSQLLocalDB;" + @"AttachDbFilename=C: \Users\NASH\Documents\Visual Studio 2015\Projects\C#\online test\online test\Database1.mdf;" + "Integrated Security=True;" + "database=<test.mdf';";
            string source_1 = @"Data Source = (LocalDB)\MSSQLLocalDB;" + @"AttachDbFilename=C:\Users\NASH\Documents\Visual Studio 2015\Projects\C#\online test\online test\test.mdf;" + "Integrated Security = True";


            SqlConnection Con_1 = new SqlConnection(source_1);
            {
                Con_1.Open();


                MessageBox.Show("connected to db");

                String sqlSelectQuery = @"SELECT * FROM[Table]";
                SqlCommand cmd = new SqlCommand(sqlSelectQuery, Con_1);
                SqlDataReader dr = cmd.ExecuteReader();

                if (dr.Read())
                {
                    //incre++;


                    {
                        label2.Text = (dr["Question"].ToString());
                        textBox1.Text = (dr["sl"].ToString());
                        radioButton1.Text = (dr["Option A"].ToString());
                        radioButton2.Text = (dr["Option B"].ToString());
                        radioButton3.Text = (dr["Option C"].ToString());
                        radioButton4.Text = (dr["Option D"].ToString());
                    }


                    incre = Convert.ToInt32(textBox1.Text);
                   // incre++;
                    // @"SELECT * FROM[Table]WHERE sl=",incre;

                }

                Con_1.Close();
            }

        }
        //button1_click is next button
        private void button1_Click(object sender, EventArgs e)
        {
           incre++;
           String sqlSelectQuery = @"SELECT * FROM[Table] WHERE sl=incre";
           if (dr.Read())
                {
                    //incre++;


                    {
                        label2.Text = (dr["Question"].ToString());
                        textBox1.Text = (dr["sl"].ToString());
                        radioButton1.Text = (dr["Option A"].ToString());
                        radioButton2.Text = (dr["Option B"].ToString());
                        radioButton3.Text = (dr["Option C"].ToString());
                        radioButton4.Text = (dr["Option D"].ToString());
                    }


        }
        // button3_click is previous button
        private void button3_Click(object sender, EventArgs e)
        {

        }

        private void button2_Click(object sender, EventArgs e)
        {

        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }
    }
}