Oracle Date Format for C#

here is my backend code, for insert record into oracle database,

in txtbook_dt.text  where am i store date.
 


    protected void btnSave_Click(object sender, EventArgs e)

    {

        string ans;

        

        ans = con.exenonqry("INSERT INTO T_LRBK(LRNO,STCODE,BOOK_DT,LRTIME,TRK_NO,DUPLNO,TRCODE,FROM_STN,TO_STN,CROSSING,CONSINEE,CONSINOR,ST_CHR,OTH_CHR,SER_CHR,RISK_CHR,HEMALI,TOT_CHR,GOOD_CHR,DELPAR,DBCODE,WT,CRCODE,G_RATE,TPACK,DONO,GOODCD,COMMOD,ACWT,LC,PF,PFAC,E_USER,CADD,CSADD,FOV,INVNO,INVVLU,TYPPACK,IN_DATE,RTYP,TOPHON,COTINNO,CITINNO)values('" + txtlrno.Text + "','" + txtstcode.Text + "','" + txtbook_dt.Text + "','" + txtlrtime.Text + "','TRKNO','" + txtdl.Text + "','TR102','" + ddlfrom_stn.SelectedValue.ToString() + "','" + ddlto_stn.SelectedValue.ToString() + "','Y','" + ddlconsignee.SelectedValue.ToString() + "','" + ddlconsignor.SelectedValue.ToString() + "','" + txtst_chr.Text + "','" + txtoth_chr.Text + "','" + txtser_chr.Text + "','" + txtrisk_chr.Text + "','" + txthemali.Text + "','" + txttotal_chr.Text + "','" + txtgood_chr.Text + "','" + txtdelpar.Text + "','" + txtdbcode.Text + "','" + txtwt.Text + "','" + txtcrcode.Text + "','" + txtg_rate.Text + "','" + txttpack.Text + "','" + txtdono.Text + "','" + ddlgoodcod.SelectedValue.ToString() + "','" + txtco.Text + "','" + txtacwt.Text + "','" + txtLC.Text + "','" + txtpf.Text + "','" + txtpfac.Text + "','" + e_user.Text + "','" + txtcadd.Text + "','" + txtcsadd.Text + "','" + txtfov.Text + "','" + txtinvno.Text + "','" + txtinvvlu.Text + "','" + txttypack.Text + "','" + txtin_date.Text + "','" + txtrtype.Text + "','" + txttophon.Text + "','" + txtcotinno.Text + "','" + txtcitinno.Text + "')");

      

        Label1.Text = ans;

        gridbind();

    }