سلام
این کارا کردم ولی به ConnectionString ارور می گیره
        private void button1_Click(object sender, EventArgs e)
{


string connetionString = null;
SqlConnection cnn ;
connetionString = "Data Source=C:\Users\somaie\Documents\Visual Studio 2010\Projects\WindowsFormsApplication3\WindowsForm sApplication3\Database1.sdf";
cnn = new SqlConnection(connetionString);
try {
cnn.Open();
MessageBox.Show ("Connection Open ! ");
cnn.Close() ;

}
catch (Exception ex)
{
MessageBox.Show("Can not open connection ! ");
}