Update profile using php - php

Question

I'm doing project and i want to update user profile using php mysql when i click
on update button it show that there are error in line 17. please help to find the error.
<?php
session_start();
if(!isset($_SESSION["n"]))
{
header("location:error.php");
}
if(isset($_POST["s"]))
{
$name=$_POST["nm"];
$lname=$_POST["lnm"];
$address=$_POST["ad"];
$u=$_SESSION["un"];
$query = "SELECT * FROM signup";
$result=mysqli_query($result,$query) or die(mysqli_connect_error());
$i=0;
while($row=mysqli_fetch_array($result))
{
$roll[$i]=$row['rollno'];
$i++;
}
$total_elmt=count($roll);
require_once("vars.php");
$conn=mysqli_connect(host,uname,pass,db) or die(mysqli_connect_error());
$query="update signup set name='$nm',lname='$lnm',address='$ad' where user_id='$value'";
$execute=mysqli_query($conn,$query);$r=mysql_affected_rows();
mysqli_close($conn);
$msg="Your information is submitted successfully";
}
?>

Answer 1

you need to open the database first to run the select query.
move this line to the top:
$conn=mysqli_connect(host,uname,pass,db) or die(mysqli_connect_error());
you are using mysqli_query function wrong. it should be
$result=mysqli_query($conn,$query) or die(mysqli_connect_error());

Answer 2

Now i have updated your code
<?php
session_start();
if(!isset($_SESSION["n"]))
{
header("location:error.php");
}
if(isset($_POST["s"]))
{
$name = $_POST["nm"];
$lname = $_POST["lnm"];
$address = $_POST["ad"];
$u = $_SESSION["un"];
$conn = mysqli_connect(host,uname,pass,db) or die(mysqli_connect_error());
$query = "SELECT * FROM signup";
$result = mysqli_query($conn, $query);
$i=0;
while($row=mysqli_fetch_array($result))
{
$roll[$i]=$row['rollno'];
$i++;
}
$total_elmt=count($roll);
require_once("vars.php");
$query="update signup set name='$nm',lname='$lnm',address='$ad' where user_id='$value'";
$execute=mysqli_query($conn,$query);
$r=mysql_affected_rows();
mysqli_close($conn);
$msg="Your information is submitted successfully";
}
?>