How Do I Find The Nearest Or Closest Numbers From Database Using C#

<pre lang="SQL">

YourTable 
studentName	Marks
Mark	        100
Tisa	        200
John	        250
Michelle	150
Parker	        450
Pete	        50
Ben	        400
Col	        325
Mis	        435
Aai	        265

First Create a Procedure Like this

CREATE PROCEDURE [dbo].[usp_FetchRecord] 
	@UserEnteredValue int
AS
BEGIN
	SET NOCOUNT ON;
	SELECT TOP 1 studentName,Marks FROM YourTable 
        WHERE Marks>=@UserEnteredValue order by Marks asc
END

-- To run the Procedure, here user has enetered 200
--EXEC [dbo].[usp_FetchRecord] 200

Result
studentName	Marks
Tisa	        200

private void button1_Click(object sender, EventArgs e)
        {
            DataTable dttable = new DataTable();
            using (var con = new      SqlConnection(ConfigurationManager.ConnectionStrings["YourConnectionString"].ConnectionString))
            using (var cmd = new SqlCommand("usp_FetchRecord", con))
            using (var da = new SqlDataAdapter(cmd))
            {
                cmd.Parameters.AddWithValue("@UserEnteredValue", textBox1.Text);
                cmd.CommandType = CommandType.StoredProcedure;
                da.Fill(dttable);
            }
            // You can use this data table dttable to get the result and display it.
        }