c# Error converting data type varchar to numeric. Sql Database : my code
 
projeservices = new HProje();
projeservices.insert("INSERT INTO ProjeEkle(İsinAdi,Yuklenici,İhaleBedeli,İhaleTarihi,SozlesmeTarihi,İsinSuresi,TeslimTarihi,BaslamaTarihi,BitisTarihi)values('" + txtisinadi.Text + "','" + txtyuklenici.Text + "','" +ntxtihalebedeli.Text + "','" +dtpihaletarihi.Text + "','" + dtpsozlesmetarihi.Text + "','" +ntxtisinsuresi.Text + "','" + dtptxtteslim.Text + "','" + dtptxtbaslama.Text + "','" + dtptxtbitis.Text + "')");
 
 
my database
 
Id	int	Unchecked
İsinAdi	nvarchar(200)	Unchecked
Yuklenici	nvarchar(200)	Unchecked
İhaleBedeli	decimal(18, 3)	Unchecked
İhaleTarihi	datetime	Unchecked
SozlesmeTarihi	datetime	Unchecked
İsinSuresi	int	Unchecked
TeslimTarihi	datetime	Unchecked
BaslamaTarihi	datetime	Unchecked
BitisTarihi	datetime	Unchecked
Unchecked
 
Can you help title also is the reason I get the error
 
 