ciao raga mi potete dire dove sbaglio per cortesia

<script type="text/javascript">
function UpdateCost() {
var sum = 0;
var gn, elem;
for (i=0; i++) {
gn = 'mama'+i;
elem = document.getElementByid(gn);
if (elem.checked == true) { sum += Number(baha[i].value); }
}
document.getElementById('totalcost').value = sum.toFixed(2);
}

</script>
</head>
<body>
<form name="ciccio">
<table width="100%" border="1">
<tr>
<td width="2%"><input name="mama[0]" type="checkbox" id='game0' onClick="UpdateCost()" value="1"></td>
<td width="92%"><input name="baha[0]" type="text" id="baha[0]" value="2"></td>
<td width="6%"></td>
</tr>
<tr>
<td><input name="mama[1]" type="checkbox" id='game1' onClick="UpdateCost()" value="1"></td>
<td><input name="baha[1]" type="text" id="baha[1]" value="3"></td>
<td></td>
</tr>
<tr>
<td><input name="mama[2]" type="checkbox" id='game2' onClick="UpdateCost()" value="1"></td>
<td><input name="baha[2]" type="text" id="baha[2]" value="4"></td>
<td></td>
</tr>
<tr>
<td><input name="mama[3]" type="checkbox" id='game3' onClick="UpdateCost()" value="1"></td>
<td><input name="baha[3]" type="text" id="baha3" value="5"></td>
<td></td>
</tr>
<tr>
<td><input name="mama[4]" type="checkbox" id='game4' onClick="UpdateCost()" value="1"></td>
<td><input name="baha[4]" type="text" id="baha4" value="6"></td>
<td></td>
</tr>
<tr>
<td></td>
<td><input name="totale" type="text" id="totalcost" value=""></td>
<td></td>
</tr>
</table>
</form>




</body>
</html>