i want to take values from my textfield into the select query please help

using (SqlCommand command = new SqlCommand("Select student.sname,admission.sroll,admission.scourse,admission.semester from admission,student where admission.asid=@Variable and admission.asid=student.sid", connection))
{
	command.Parameters.Add(new SqlParameter("Variable", txtVariable.Text.Trim()));
	SqlDataReader reader = command.ExecuteReader();
	DataTable dataTable = new DataTable();
	dataTable.Load(reader); 
}