how to use compare validator for windows forms application?

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Visual-Studio

(I want to add validator for entering balance....if we enter value less than 1000 it should show some message)
private void button1_Click(object sender, EventArgs e)
{
Regex expr = new Regex(@"^((\+){0,1}91(\s){0,1}(\-){0,1}(\s){0,1}){0,1}9[0-9](\s){0,1}(\-){0,1}(\s){0,1}[1-9]{1}[0-9]{7}$");
if (expr.IsMatch(textBox4.Text) == false)
{
label14.Text = "Enter Valid Mobile No";
}
Regex expr1 = new Regex(@"^[a-zA-Z][\w\.-]{2,28}[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$");
if (expr1.IsMatch(textBox3.Text) == false)
label13.Text = "Enter Valid Email";
if (textBox6.TextLength < 4)
label12.Text="PIN should have only 4 digits";
if (textBox6.TextLength > 4)
label12.Text = "PIN should have only 4 digits";
else
{
SqlConnection con = new SqlConnection(@"data source=ABHINAV-PC\ABHI;integrated security=true;initial catalog=ATM;");
con.Open();
SqlCommand cmd = new SqlCommand("insert into customer_details(name,address,email_id,contact_number,card_number,pin,city,account_type,balance) values('" + textBox1.Text + "','" + textBox2.Text + "','" + textBox3.Text + "','" + textBox4.Text + "','" + textBox5.Text + "','" + textBox6.Text + "','" + textBox7.Text + "','" + comboBox1.Text + "','" + textBox9.Text + "')", con);
cmd.ExecuteNonQuery();
comboBox1.Text = " ";
textBox9.Text = " ";
textBox8.Text = " ";
textBox7.Text = " ";
textBox6.Text = " ";
textBox5.Text = " ";
textBox4.Text = " ";
textBox3.Text = " ";
textBox2.Text = " ";
textBox1.Text = " ";
textBox1.Focus();
con.Close();
}
}