Okay, I am making a market feature for my new game. I want users to be able to choose one of the 4 different resources to trade for another resource. The resources have different, changing conversion rates. I want them to be able to selectct what resource to trade and input how much to trade of it. Then to select (from a dropdown list) what resource to trade for and then click the calculate button and it will show them how much they will get of the second resource.

Example:

Gold: 0.75%
Wood: 1.38%
Food: 1.22%
Stone: 0.99%

Trade 1000 units of Gold
Get ____ units of food.

So the javascript would need to be able to take 1.22 - .75, then subtract that from 1, then multiply that by 1000 (the specified amount of gold) and show that number.

Here was my attempt at it:

<form name="market" action="http://eternalkingdoms.com/process_binfo.php?id=market" method="post">
<b>Trade:</b><br>
<select name="resource_1">
<option value="gold" onclick="setVal_1(<?=$gold?>)">Gold</option>
<option value="wood" onclick="setVal_1(<?=$wood?>)">Wood</option>
<option value="food" onclick="setVal_1(<?=$food?>)">Food</option>
<option value="stone" onclick="setVal_1(<?=$stone?>)">Stone</option>
</select>
<input type="text" size="11" maxlength="11" name="amount_1"
class="forms" onkeyup="return addem(this.form)"><font size="1">(amount)</font>
<br>
<b>For:</b><br>
<select name="resource_2">
<option value="gold" onclick="setVal_2(<?=$gold?>)">Gold</option>
<option value="wood" onclick="setVal_2(<?=$wood?>)">Wood</option>
<option value="food" onclick="setVal_2(<?=$food?>)">Food</option>
<option value="stone" onclick="setVal_2(<?=$stone?>)">Stone</option>
</select>
<input type="text" size="11" class="forms" readonly><font size="1">(amount)</font><br>
<input type="button" onclick="calcIt()" value="Calculate" class="forms">
<input type="submit" value="Trade" class="forms">
</form>
<script>
var _val_1 = <?=$gold?>;
function setVal_1(_a_1) {_val_1=_a_1;}
var _val_2 = <?=$gold?>;
function setVal_2(_a_2) {_val_2=_a_2;}
function calcIt() {
_sub = _val_2-_val_1;
_val = 1-_sub;
_v = parseInt(document.market.amount_1.value);
document.market.amount_2.value=_v*_val;
}
</script>

Someone helpedme resolve it over instant messenger.

Final code:


<form name="market" action="http://eternalkingdoms.com/process_binfo.php?id=market" method="post">
<b>Trade:</b><br>
<select name="resource_1" onclick="setVal_1(this.options[this.selectedIndex].value);">
<option value="gold">Gold</option>
<option value="wood">Wood</option>
<option value="food">Food</option>
<option value="stone">Stone</option>
</select>
<input type="text" size="11" maxlength="11" name="amount_1" class="forms"><font size="1">(amount)</font>
<br>
<b>For:</b><br>
<select name="resource_2" onclick="setVal_2(this.options[this.selectedIndex].value);">
<option value="gold">Gold</option>
<option value="wood">Wood</option>
<option value="food">Food</option>
<option value="stone">Stone</option>
</select>
<input type="text" name="amount_2" size="11" class="forms" readonly><font size="1">(amount)</font><br>
<input type="button" onclick="calcIt()" value="Calculate" class="forms">
<input type="submit" value="Trade" class="forms">
</form>
<script type="text/javascript" language="javascript">
materials = new Array();
materials["gold"] = <?=$gold?>;
materials["wood"] = <?=$wood?>;
materials["food"] = <?=$food?>;
materials["stone"] = <?=$stone?>;

var _val_1 = materials["gold"];
function setVal_1(_a_1) {
_val_1 = materials[_a_1];
}

var _val_2 = materials["gold"];
function setVal_2(_a_2) {
_val_2 = materials[_a_2];
}

function calcIt() {
_sub = _val_2-_val_1;
_val = 1-_sub;

_v = parseInt(document.forms["market"].elements["amount_1"].value);
document.forms["market"].elements["amount_2"].value = _v*_val;
}
</script>