validate the condition

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C#5.0

My run mode as follows

i have one dropdownlist as follows i have one text box as follows textbox1
Change Name textbox1 53248
Change COC
Change Grade

Suppose when user select the Change Name from dropdownlist and click show button record shown in gridview
Show Button code as follows

if (ddlType.SelectedItem.ToString() != "" || txtstudid.Text.ToString().Trim() == "")
          {
   Sql = "select Type,Reason,User_ID as Users,Crt_date from Admin_Track where Type ='"+ Type.ToString().Trim() + "'";
              dt = SCon.ReadSql_DT(Sql);
              if (dt.Rows.Count > 0)

                  gvAdminrpt.DataSource = dt;
                  gvAdminrpt.DataBind();
                  Cache["data"] = dt;
         }

Similarily Suppose when type the student id in textbox1 and click show button for that partiuclar record shown in gridview

if (txtstudid.Text.ToString() !="" && ddlType.SelectedItem.ToString() == "")
        {
            
            Sql = "select Type,Reason,User_ID as Users,Crt_date from Admin_Track where Reason like '%"  + txtstudid.Text.ToString().Trim() + "%'";
            dt = SCon.ReadSql_DT(Sql);
            if (dt.Rows.Count > 0)
                gvAdminrpt.DataSource = dt;
                gvAdminrpt.DataBind();
                Cache["data"] = dt;
        }