Conditional registration to database

It seems like you are trying to insert student records into a database and handle the parent's phone numbers based on certain conditions. Your code is close to achieving this, but there are a few issues and improvements you can make:

1. Declare the val9 variable outside the conditional statements so that it's accessible throughout the scope of your code.

2. Use parameterized queries to prevent SQL injection vulnerabilities.

Here's an improved version of your code:

foreach (int j in ChkedRow)
{
    var val1 = dataGridView1.Rows[j].Cells["tcno"].Value;
    var val2 = dataGridView1.Rows[j].Cells["ono"].Value;
    var val3 = dataGridView1.Rows[j].Cells["isim"].Value;
    var val4 = dataGridView1.Rows[j].Cells["soyisim"].Value;
    var val5 = dataGridView1.Rows[j].Cells["cinsiyet"].Value;
    var val6 = dataGridView1.Rows[j].Cells["dtarihi"].Value;
    var val7 = dataGridView1.Rows[j].Cells["sinifi"].Value;
    var val8 = dataGridView1.Rows[j].Cells["unvan"].Value;
    var val10 = dataGridView1.Rows[j].Cells["kbaskani"].Value;
    
    string val9 = null;

    if (!String.IsNullOrEmpty(dataGridView1.Rows[j].Cells["atel"].Value.ToString()))
    {
        val9 = dataGridView1.Rows[j].Cells["atel"].Value.ToString();
    }
    else if (!String.IsNullOrEmpty(dataGridView1.Rows[j].Cells["btel"].Value.ToString()))
    {
        val9 = dataGridView1.Rows[j].Cells["btel"].Value.ToString();
    }
    else
    {
        MessageBox.Show("'" + val3 + " " + val4 + "' isimli ögrencilerin veli telefonu bulunmamaktadir.");
        continue; // Use continue to move to the next iteration instead of return
    }

    using (OleDbConnection conn = new OleDbConnection(connectionString))
    {
        conn.Open();
        
        var cmdText = "INSERT INTO gezilistemiz25 (tcno, ono, adi, soyadi, cinsiyet, dtarihi, sinifi, unvani, vtel, kbaskani) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)";
        var command = new OleDbCommand(cmdText, conn);
        command.Parameters.AddWithValue("tcno", val1);
        command.Parameters.AddWithValue("ono", val2);
        command.Parameters.AddWithValue("adi", val3);
        command.Parameters.AddWithValue("soyadi", val4);
        command.Parameters.AddWithValue("cinsiyet", val5);
        command.Parameters.AddWithValue("dtarihi", val6);
        command.Parameters.AddWithValue("sinifi", val7);
        command.Parameters.AddWithValue("unvani", val8);
        command.Parameters.AddWithValue("vtel", val9);
        command.Parameters.AddWithValue("kbaskani", val10);
        
        command.ExecuteNonQuery();
    }
}

In this code:

• I've declared val9 outside the conditional statements so that it's accessible later when constructing the SQL command.
• I've used parameterized queries to make your SQL statements safer and prevent SQL injection attacks.
• I've used using blocks for the OleDbConnection to ensure proper disposal and management of resources.

Please replace "connectionString" with your actual database connection string.

This code will insert student records into the database, taking the mother's phone number if available, the father's phone number if not, and showing a message if neither is available for a student.