function set_global_var($var, $data)
{
    global $session;
    global $specialinc;
    $query = "SELECT * FROM globalvars WHERE variable='{$var}'";
    $res = db_query($query) or die(db_error($link));
    if (db_num_rows($res)) {
        $query = "UPDATE globalvars SET data='{$data}' WHERE variable='{$var}'";
    } else {
        $query = "INSERT INTO globalvars (variable, data)\n                    VALUES ('{$var}', '{$data}') ";
    }
    if ($data === NULL) {
        $query = "DELETE FROM globalvars WHERE variable='{$var}'";
    }
    $res = db_query($query) or die(db_error($link));
    $retval = get_global_var($var);
    return $retval;
}
<?php

/***************************************************************************
//  Gem Exchange v1.0
//  Coded by: Turock
//  Allows players to exchange gems for gold
***************************************************************************/
require_once "common.php";
// exchange rate for gems
$ex_rate = get_global_var(ExchangeRate);
page_header("Gem Exchange");
addnav("Sell your Gems", "gemshop.php?op=sell");
addnav("Return to the Village", "village.php");
$gemsell = $session['user']['gems'];
output("`n`^You enter the shop and see an old man sitting behind a small counter.`n");
output("He doesn't say anything and instead points to a small sign...`n");
output("`nThe sign reads:  `%Gem Exchange Rate Today: `&1 `^gem = `%" . commas($ex_rate) . " `^gold");
if ($HTTP_GET_VARS['op'] == "sell") {
    if ($session['user']['gems'] < 1) {
        output("`n`nYou don't have any gems to sell.`n");
    } else {
        $word = "gems";
        if ($session['user']['gems'] == 1) {
            $word = "gem";
        }
        output("`n`n`^You have `&{$gemsell} `^{$word} to sell.`n");
        output("`%How many would you like to sell?`n");
        output("<form action='gemshop.php?op=sell2' method='POST'><input name='sell' id='sell'><input type='submit' class='button' value='sell'></form>", true);
        addnav("", "gemshop.php?op=sell2");
    }
}