How to pass integer variable in sql query

You have to add a parameter:

int no = FormView1.PageIndex;
SqlCommand cmd = 
    new SqlCommand("select Answer from Questions where QuestionNo = @no", cn);

// Set the parameter up before executing the command
cmd.Parameters.Add("@no", SqlDbType.Int);
cmd.Parameters["@no"].Value = no;

You need to add a SqlParameter to the SqlCommand:

int no = FormView1.PageIndex;
SqlCommand cmd = new SqlCommand("select Answer from Questions where QuestionNo = @no", cn);
cmd.Parameters.AddWithValue("@no", no);

use an array of System.Data.SqlClient.SqlParameter

SqlCommand cmd(...);
SqlParameter[] inQueryParameters = ...;
cmd.Parameters.AddRange(inQueryParameters);

Use SqlParameters. See the example below.

http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.parameters.aspx

You can use this code:

SqlCommand ageCom = new SqlCommand("select age_phase from PatintInfo where patient_ID=@ptn_id", con);
ageCom.Parameters.Add("@ptn_id",SqlDbType.Int).Value=Convert.ToInt32(TextBox1.Text);

It had worked in my program correctly.