Como restar valores de un formulario con php y mysql?

[xagentex]

Ok los codigos son los siguientes:

index.php

Código:

<?php require_once('Connections/conex.php'); ?>
<?php
//initialize the session
if (!isset($_SESSION)) {
  session_start();
}

// ** Logout the current user. **
$logoutAction = $_SERVER['PHP_SELF']."?doLogout=true";
if ((isset($_SERVER['QUERY_STRING'])) && ($_SERVER['QUERY_STRING'] != "")){
  $logoutAction .="&". htmlentities($_SERVER['QUERY_STRING']);
}

if ((isset($_GET['doLogout'])) &&($_GET['doLogout']=="true")){
  //to fully log out a visitor we need to clear the session varialbles
  $_SESSION['MM_Username'] = NULL;
  $_SESSION['MM_UserGroup'] = NULL;
  $_SESSION['PrevUrl'] = NULL;
  unset($_SESSION['MM_Username']);
  unset($_SESSION['MM_UserGroup']);
  unset($_SESSION['PrevUrl']);
	
  $logoutGoTo = "login.php";
  if ($logoutGoTo) {
    header("Location: $logoutGoTo");
    exit;
  }
}
?>
<?php
if (!isset($_SESSION)) {
  session_start();
}
$MM_authorizedUsers = "Nivel 1,Nivel 2";
$MM_donotCheckaccess = "false";

// *** Restrict Access To Page: Grant or deny access to this page
function isAuthorized($strUsers, $strGroups, $UserName, $UserGroup) { 
  // For security, start by assuming the visitor is NOT authorized. 
  $isValid = False; 

  // When a visitor has logged into this site, the Session variable MM_Username set equal to their username. 
  // Therefore, we know that a user is NOT logged in if that Session variable is blank. 
  if (!empty($UserName)) { 
    // Besides being logged in, you may restrict access to only certain users based on an ID established when they login. 
    // Parse the strings into arrays. 
    $arrUsers = Explode(",", $strUsers); 
    $arrGroups = Explode(",", $strGroups); 
    if (in_array($UserName, $arrUsers)) { 
      $isValid = true; 
    } 
    // Or, you may restrict access to only certain users based on their username. 
    if (in_array($UserGroup, $arrGroups)) { 
      $isValid = true; 
    } 
    if (($strUsers == "") && false) { 
      $isValid = true; 
    } 
  } 
  return $isValid; 
}

$MM_restrictGoTo = "login.php";
if (!((isset($_SESSION['MM_Username'])) && (isAuthorized("",$MM_authorizedUsers, $_SESSION['MM_Username'], $_SESSION['MM_UserGroup'])))) {   
  $MM_qsChar = "?";
  $MM_referrer = $_SERVER['PHP_SELF'];
  if (strpos($MM_restrictGoTo, "?")) $MM_qsChar = "&";
  if (isset($_SERVER['QUERY_STRING']) && strlen($_SERVER['QUERY_STRING']) > 0) 
  $MM_referrer .= "?" . $_SERVER['QUERY_STRING'];
  $MM_restrictGoTo = $MM_restrictGoTo. $MM_qsChar . "accesscheck=" . urlencode($MM_referrer);
  header("Location: ". $MM_restrictGoTo); 
  exit;
}
?>
<?php
if (!function_exists("GetSQLValueString")) {
function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "") 
{
  if (PHP_VERSION < 6) {
    $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;
  }

  $theValue = function_exists("mysql_real_escape_string") ? mysql_real_escape_string($theValue) : mysql_escape_string($theValue);

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;    
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? doubleval($theValue) : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}
}

$colname_login = "-1";
if (isset($_SESSION['MM_Username'])) {
  $colname_login = $_SESSION['MM_Username'];
}
mysql_select_db($database_conex, $conex);
$query_login = sprintf("SELECT * FROM usuarios WHERE usuario = %s", GetSQLValueString($colname_login, "text"));
$login = mysql_query($query_login, $conex) or die(mysql_error());
$row_login = mysql_fetch_assoc($login);
$totalRows_login = mysql_num_rows($login);
$_SESSION['name'] = $row_login['name'];


mysql_select_db($database_conex, $conex);
$res=mysql_query("SELECT precio FROM autogestion WHERE usuario = '".$_SESSION['MM_Username']."'");
while($row=mysql_fetch_assoc($res))
$total-=$row['precio'];

?>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>.:Sistema de Autogestion Virtual:.</title>

<link href="css/estilos.css" rel="stylesheet" type="text/css">
<link href="fonts/style.css" rel="stylesheet" type="text/css">
</head>
<body background="images/bground.jpg" oncontextmenu="return false">

<div id="container">
<div id="header"><div id="logo">Sistema de Autogestion Virtual</div>
<div id="botones">
    <ul>  
		<li><a href="<?php echo $logoutAction ?>"><span class=" icon-swich"></span> Salir</a></li>  
		<li><a href="contacto.php" target="link"><span class=" icon-phone"></span> Contacto</a></li>
		<li><a href="registrar_pago.php" target="link"><span class="icon-credit-card"></span> Registrar Pago</a></li>
		<li><a href="perfil_de_usuario.php?usuario=<?php echo $_SESSION['MM_Username']; ?>" target="link"><span class="icon-user"></span> Perfil</a></li>
        <li><a href="index.php"><span class="icon-home"></span> Inicio</a></li>

    </ul>
    </div></div>
  <div id="main">
  <div id="notificacion"><div id="nombre"><div id="welcome">Bienvenido <?php echo $_SESSION['name']; ?></div></div><div id="search"></div><div id="precio"><div id="saldo">Su Saldo Es: <?php echo $total; ?> Bs.</div></div></div>
	<div id="menu">
    <div id="titulo">Menu Principal</div>
    <div id="nav">
    <ul>    
        <li><a href="activacion_de_lineas.php" target="link">Activacion de Lineas</a></li>
        <li><a href="lineas.php" target="link">Lineas HEX y MEID</a></li>
        <li><a href="cambio_de_serial.php" target="link">Cambio de Serial</a></li>
        <li><a href="cambio_de_plan.php" target="link">Cambio de Plan</a></li>
        <li><a href="servicios_de_datos.php" target="link">Servicios de Datos</a></li>
        <li><a href="consulta_de_datos.php" target="link">Consulta de Datos</a></li>
		<li><a href="recarga_de_saldo.php" target="link">Recarga de Saldo</a></li>
        <li><a href="actualizacion_de_datos.php" target="link">Actualizacion de Datos</a></li>
        <li><a href="consulta_negativo.php" target="link">Consulta de Negativos</a></li>
        <li><a href="agl.php" target="link">Atencion en Linea</a></li>
        <li><a href="http://ovam.movilnet.com.ve/OvamExtranet/Vistas/validar_usuario2.php" target="link">Extranet de Agentes</a></li>
 
    </ul>
    </div></div>
      <div id="contenido">
        <iframe src="listar.php" scrolling="auto"  name="link" frameborder="0">	</iframe>
      </a></div>
      <div id="footer">Diseñado Por Campos Technology &copy; 2017 Todos Los Derechos Reservados</div>
																																																																																															
  </div>
</div>
</body>
</html>
<?php
mysql_free_result($login);
?>