regarding an sql query error - asp.net

Question

here is my admin.aspx.vb
Imports System.Data.SqlClient
Partial Class Admin
Inherits System.Web.UI.Page
Dim conn As New SqlConnection("Data Source=CHIRAG-PC;Initial Catalog=car;Integrated Security=True")
Dim cmd As SqlCommand
Dim drd As SqlDataReader
Dim adp As SqlDataAdapter
Dim y As String
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
End Sub
Protected Sub GridView1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles GridView1.SelectedIndexChanged
Dim x As Integer
x = GridView1.SelectedIndex
y = GridView1.Rows(x).Cells(1).Text
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim str As String
str = "update carHeader set cartype='" + car.Text.ToString() + "',imagefile='" + img.Text + "',capacity=" + cap.Text + "where id=" + Convert.ToDouble(y)
conn.Open()
cmd = New SqlCommand(str, conn)
cmd.ExecuteNonQuery()
conn.Close()
End Sub
End Class
and its admin.aspx
<%# Page Title="" Language="VB" MasterPageFile="~/MasterPage.master" AutoEventWireup="false" CodeFile="Admin.aspx.vb" Inherits="Admin" %>
<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" Runat="Server">
<br />
<br />
</asp:Content>
<asp:Content ID="Content2" runat="server" contentplaceholderid="MainContent">
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="Data Source=CHIRAG-PC;Initial Catalog=car;Integrated Security=True"
ProviderName="System.Data.SqlClient"
SelectCommand="SELECT * FROM [carHeader] ORDER BY [id]"></asp:SqlDataSource>
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
DataSourceID="SqlDataSource1" Height="149px" Width="267px">
<Columns>
<asp:CommandField ShowSelectButton="True" />
<asp:BoundField DataField="id" HeaderText="id"
SortExpression="id" />
<asp:BoundField DataField="cartype" HeaderText="cartype"
SortExpression="cartype" />
<asp:BoundField DataField="imagefile" HeaderText="imagefile"
SortExpression="imagefile" />
<asp:BoundField DataField="capacity" HeaderText="capacity"
SortExpression="capacity" />
</Columns>
</asp:GridView>
<asp:Panel ID="Panel1" runat="server">
<asp:Label ID="Label1" runat="server" Text="Image file"></asp:Label>
<asp:TextBox ID="img" runat="server"></asp:TextBox>
<asp:Label ID="Label2" runat="server" Text="Car Type"></asp:Label>
<asp:TextBox ID="car" runat="server"></asp:TextBox>
<asp:Label ID="Label3" runat="server" Text="capacity"></asp:Label>
<asp:TextBox ID="cap" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Save" />
</asp:Panel>
</asp:Content>
getting an error in sql query regarding its update statement
and table contents are of carHeader:
cartype varchar ,id int,imagefile varchar,capacity int

Answer 1

... + cap.Text + "where ...
Notice the lack of a space before where. It's probably producing a statement like:
... field = valuewhere ...
This would break the SQL.
Additionally, it's bad practice to use string concatenation in SQL statements like this, both from a security and performance point of view. You'll want to look into using parameterized queries.
Edit: Based on your comment here:
its givin me error conversion from update set cartype=....to double type is not valid
It sounds like the error is referring to this part of the query:
set cartype='" + car.Text.ToString() + "'
What type is cartype? According to the error message, it's a double. But according to your query, you're trying to set it to a string value (by wrapping it in single quotes). If it's a double then it needs to be a numeric value, not a string.