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I am a university student. What are the sample programs we can do with php? Can those who have php codes share about this subject? Thanks in advance

Hi, I am currently working on completing an online computer science course, and am in the last few weeks, with just a few programs left, but that said time is of the essence. What I am working on right now is a program that will let you buy and sell stocks. No transactions actually occur, it only looks like you are buying and selling. I was given a framework to start with, here I have linked to a example completed project: http://finance.cs50.net/login.php I am getting close, but am having some trouble with the "buy" function. Here is my php code for buy: <?php // configuration require("../includes/config.php"); // if form was submitted if ($_SERVER["REQUEST_METHOD"] == "POST") { if (((empty($_POST["symbol"])) == True) || ((empty($_POST["shares"])) == True)) { apologize("You MUST enter the Symbol, and ammount of stock that you want!"); } else if (preg_match("/^\d+$/", $_POST["shares"]) == False) { apologize("You must enter a postive whole number for the number of shares you want to buy!"); } else { $stock = lookup($_POST["symbol"]); $rows = query("SELECT LAST_INSERT_ID() AS id"); $id = $rows[0]["id"]; INSERT INTO table (id, symbol, shares) VALUES(7, , 10) ON DUPLICATE KEY UPDATE shares = shares + VALUES(shares) redirect("index.php"); } } else { // else render form render("buy_stock.php", ["title" => "Buy "]); } ?> And here is the code for the html front page of buy: <form action="buy.php" method="post"> <fieldset> <div class="control-group"> <input autofocus name="symbol" placeholder="SYMBOL" type="text"/> </div> <div class="control-group"> <input name="shares" placeholder="Number of shares" type="int"/> </div> <div class="control-group"> <button type="submit" class="btn">BUY</button> </div> </fieldset> </form> <div> or <a href="index.php">Home Page</a> </div> Here is a program defining functions, this program was provided buy the course: <?php /*********************************************************************** * functions.php * * Computer Science 50 * Problem Set 7 * * Helper functions. **********************************************************************/ require_once("constants.php"); /** * Apologizes to user with message. */ function apologize($message) { render("apology.php", ["message" => $message]); exit; } /** * Facilitates debugging by dumping contents of variable * to browser. */ function dump($variable) { require("../templates/dump.php"); exit; } /** * Logs out current user, if any. Based on Example #1 at * http://us.php.net/manual/en/function.session-destroy.php. */ function logout() { // unset any session variables $_SESSION = array(); // expire cookie if (!empty($_COOKIE[session_name()])) { setcookie(session_name(), "", time() - 42000); } // destroy session session_destroy(); } /** * Returns a stock by symbol (case-insensitively) else false if not found. */ function lookup($symbol) { // reject symbols that start with ^ if (preg_match("/^\^/", $symbol)) { return false; } // reject symbols that contain commas if (preg_match("/,/", $symbol)) { return false; } // open connection to Yahoo $handle = @fopen("http://download.finance.yahoo.com/d/quotes.csv?f=snl1&s=$symbol", "r"); if ($handle === false) { // trigger (big, orange) error trigger_error("Could not connect to Yahoo!", E_USER_ERROR); exit; } // download first line of CSV file $data = fgetcsv($handle); if ($data === false || count($data) == 1) { return false; } // close connection to Yahoo fclose($handle); // ensure symbol was found if ($data[2] === "0.00") { return false; } // return stock as an associative array return [ "symbol" => $data[0], "name" => $data[1], "price" => $data[2], ]; } /** * Executes SQL statement, possibly with parameters, returning * an array of all rows in result set or false on (non-fatal) error. */ function query(/* $sql [, ... ] */) { // SQL statement $sql = func_get_arg(0); // parameters, if any $parameters = array_slice(func_get_args(), 1); // try to connect to database static $handle; if (!isset($handle)) { try { // connect to database $handle = new PDO("mysql:dbname=" . DATABASE . ";host=" . SERVER, USERNAME, PASSWORD); // ensure that PDO::prepare returns false when passed invalid SQL $handle->setAttribute(PDO::ATTR_EMULATE_PREPARES, false); } catch (Exception $e) { // trigger (big, orange) error trigger_error($e->getMessage(), E_USER_ERROR); exit; } } // prepare SQL statement $statement = $handle->prepare($sql); if ($statement === false) { // trigger (big, orange) error trigger_error($handle->errorInfo()[2], E_USER_ERROR); exit; } // execute SQL statement $results = $statement->execute($parameters); // return result set's rows, if any if ($results !== false) { return $statement->fetchAll(PDO::FETCH_ASSOC); } else { return false; } } /** * Redirects user to destination, which can be * a URL or a relative path on the local host. * * Because this function outputs an HTTP header, it * must be called before caller outputs any HTML. */ function redirect($destination) { // handle URL if (preg_match("/^https?:\/\//", $destination)) { header("Location: " . $destination); } // handle absolute path else if (preg_match("/^\//", $destination)) { $protocol = (isset($_SERVER["HTTPS"])) ? "https" : "http"; $host = $_SERVER["HTTP_HOST"]; header("Location: $protocol://$host$destination"); } // handle relative path else { // adapted from http://www.php.net/header $protocol = (isset($_SERVER["HTTPS"])) ? "https" : "http"; $host = $_SERVER["HTTP_HOST"]; $path = rtrim(dirname($_SERVER["PHP_SELF"]), "/\\"); header("Location: $protocol://$host$path/$destination"); } // exit immediately since we're redirecting anyway exit; } /** * Renders template, passing in values. */ function render($template, $values = []) { // if template exists, render it if (file_exists("../templates/$template")) { // extract variables into local scope extract($values); // render header require("../templates/header.php"); // render template require("../templates/$template"); // render footer require("../templates/footer.php"); } // else err else { trigger_error("Invalid template: $template", E_USER_ERROR); } } ?> I have been working on getting BUY working for the whole day, but have had nothing but errors... Does anything jump out as a problem to anyone??? If I haven't given you enough info, please let me know! Thanks in advance, I really am stuck on this one, and am running out of time, as this is not my last program. Josh