System.Data.DataColumn.ToString C# (CSharp) Method

        public override string ToString() => _expression == null ?
            ColumnName :
            ColumnName + " + " + Expression;

        private void btnSearch_Click(object sender, EventArgs e)
        {
            float  CrossSectionArea = -1;
            int    TypeCode         = -1;
            string strFilter        = "";
            bool   check            = false;

            if (chkMaterail.Checked)
            {
                TypeCode = Convert.ToInt32(cboMaterial.SelectedValue);

                strFilter = " Type='" + TypeCode.ToString() + "'";
                check     = true;
            }
            if (chkSectionArea.Checked)
            {
                CrossSectionArea = Convert.ToSingle(nudCrossSectionArea.Value.ToString());
                if (strFilter != "")
                {
                    strFilter += " AND CrossSectionArea='" + CrossSectionArea.ToString() + "'";
                }
                else
                {
                    strFilter = " CrossSectionArea='" + CrossSectionArea.ToString() + "'";
                }
                check = true;
            }
            if (check)
            {
                //DataView dv = new DataView();
                //dv.Table = dtMerge;
                //dv.RowFilter = strFilter;
                dtMerge.DefaultView.RowFilter   = strFilter;
                gvConductor.AutoGenerateColumns = false;
                gvConductor.DataSource          = dtMerge;
            }
            else
            {
                dtMerge.DefaultView.RowFilter = "";
                //gvConductor.AutoGenerateColumns = false;
                //gvConductor.DataSource = dtMerge;
            }
            Atend.Global.Utility.UBinding.SetGridToCurrentSelectedEquip("CabelTipCode", new object[1] {
                selectedProductCode
            }, dtMerge, gvConductor, this);
            ChangeColor();
            //BindDataToCounductorTip();
            for (int i = 0; i < gvConductor.Rows.Count; i++)
            {
                if (Convert.ToInt32(gvConductor.Rows[i].Cells[1].Value.ToString()) == selectedProductCode && Convert.ToBoolean(gvConductor.Rows[i].Cells[4].Value.ToString()) == false)
                {
                    gvConductor.Rows[i].DefaultCellStyle.BackColor = Color.Yellow;
                }
            }

            //BindDataToCounductorTip();
        }