Checkbox per row
http://stackoverflow.com/questions/32391400/gridview-webform-having-multiple-checkboxes-per-row-but-only-1-per-row-is-allowe/32391624#32391624
HTML
<tr bgcolor=$warna><td>$nu</td><td>$data[pertanyaan]</td>
<td><input type=checkbox name=cek1[] value=$data[id] id=id1 onclick='enableDisableAll(this)'></td>
<td><input type=checkbox name=cek2[] value=$data[id] id=id2 onclick='enableDisableAll(this)'></td>
<td><input type=checkbox name=cek3[] value=$data[id] id=id3 onclick='enableDisableAll(this)'></td>
<td><input type=checkbox name=cek4[] value=$data[id] id=id4 onclick='enableDisableAll(this)'></td>
JavaScript
function enableDisableAll(e) {
var own = e;
var form = document.getElementById("checkbox");
var elements = form.elements;
//var id=$(this).data("id");
for (var i = 0 ; i < elements.length ; i++) {
if(own !== elements[i] ){
if(own.checked == true){
elements[i].disabled = true;
}else{
elements[i].disabled = false;
}
}
}
}