Visual Studio Syntax

你能帮我了解一下Visual studio c#的语法吗我想要我的电话目录，如果你在主键中输入相同的数据，它会显示一个显示"已经存在"的显示消息框，如果它不是，它会恢复正常功能…好吧，我一直在尝试，但我不能弄清楚…

con.Open();
       if (!dataGridView1.Equals(textBox3.Text)) 
        { 
        SqlCommand cmd = new SqlCommand (@"INSERT INTO Amer
                     (First, Last, Mobile, Email, Category)
                     VALUES        ('" + textBox1.Text + "','" + textBox2.Text + "','" + textBox3.Text + "','" + textBox4.Text + "','" + comboBox1.Text + "')",con);
        cmd.ExecuteNonQuery();
        MessageBox.Show("Saved!");
        textBox1.Text = "";
        textBox2.Clear();
        textBox3.Text = "";
        textBox4.Clear();
        comboBox1.SelectedIndex = -1;
        textBox1.Focus();
        Display();

       }
            else
            {
                MessageBox.Show("Mobile Number Already Exist!");
                textBox1.Text = "";
                textBox2.Clear();
                textBox3.Text = "";
                textBox4.Clear();
                comboBox1.SelectedIndex = -1;
                textBox1.Focus();
                Display();