dbconnect php

<?php
$server_addr="localhost";
$server_user="root";
$server_pass="";
$dbname="injection";

function dbconnect(){
  $conn= new mysqli($GLOBALS['server_addr'],$GLOBALS['server_user'],$GLOBALS['server_pass'],$GLOBALS['dbname']);
  if ($conn->connect_errno){
    return False;
  }
  else{
    return $conn;
  }
}

function statementop($db,$username,$password){
#return "I" if injection is detected
#return "S" if successfull
#return "F" if user not found

  $statement=$db->prepare("SELECT username,password FROM users WHERE username=? AND password=?;");
    $statement->bind_param("ss",$username,$password);
    $statement->execute();
    $result = $statement->get_result();
    if($result){
    while ($row = $result->fetch_array(MYSQLI_ASSOC))
          {
            if($row["username"]==$username && $row["password"]==$password){
              return "S";
            }
            else{
              return "F";
            }
          }
        }
  $result->free();
  $statement->close();
    /*if(is_null($result)){
      return "S";
    }
    else{
      return "F";
    }
  }*/
  $statement->close();
}
?>