1. ## How to retrieve value based on radiobutton?

How I can retrieve value based on radiobutton

This is my code

Code:
```<script type="text/javascript">
function MyCalc(){

var r = document.SignupForm.r.value;
var q = document.SignupForm.q.value;
var s = document.SignupForm.s.value;
var n = document.SignupForm.n.value;

var a = (q*n)/s;
var b = 1/2;

var woc   = r-1;
var total = Math.pow(a,b);

document.SignupForm.n1.value = round(n);
document.SignupForm.total.value = round(total);
document.SignupForm.woc.value = round(woc);

function round(x)
{
return Math.round(x*100)/100;
}
//Qn/s^1/2 ==> (Q*n)/s^(1/2) and width of channel,B = R-1
//flow depth, y ==> we get from graph

}</script>

<table>
<tr>
<th width="19%"><div align="right">Drainage Reserved Width, R =</div></th>
<th width="5%">&nbsp;</th>
<th width="76%"><div align="left">
<label>
<input name="r" type="text" size="32"/>
</label>
m</div></th>
</tr>
<tr>
<th><div align="right">Design Flow Q =</div></th>
<td>&nbsp;</td>
<td><div align="left">
<label>
<input name="q" type="text" size="32" />
</label>
m 3/s</div></td>
</tr>
<tr>
<th><div align="right">Longitudinal Slope, s =</div></th>
<td>&nbsp;</td>
<td><div align="left">
<label>
<input name="s" type="text" size="32" />
</label>
m</div></td>
</tr>
<tr>
<th><div align="right">Side Slope, Z =</div></th>
<td>&nbsp;</td>
<td><div align="left">
<label>
<input name="z" type="text" size="32" />
</label>
</div></td>
</tr>
<tr>
<th><div align="right">Manning's, n =</div></th>
<td>&nbsp;</td>
<td><div align="left">
<label>
<input name="n1" type="text" id="n1" size="32" />
</label>
</div></td>
</tr>
</table>
<br />
<table class="tbl_brdr">
<tr>
<th rowspan="2">Surface Grass Cover</th>
<th colspan="2">Suggested n Values</th>
</tr>
<tr>
<th>Min</th>
<th>Max</th>
</tr>
<tr>
<th>Short Grass Cover</th>
<td><label>
<input type="radio" name="n"  value="0.030" onChange="MyCalc()" />
0.030</label></td>
<td><label>
<input type="radio" name="n" value="0.035" onChange="MyCalc()" />
</label>
0.035</td>
</tr>
<tr>
<th>Tall Grass Cover</th>
<td><label>
<input type="radio" name="n"  value="0.035" onChange="MyCalc()" />
0.035</label></td>
<td><label>
<input type="radio" name="n"  value="0.050" onChange="MyCalc()" />
0.050</label></td>
</tr>
</table>

<table width="908" class="tbl_brdr">
<tr>
<th width="179"><div align="right">Qn/s^ 1/2 =</div></th>
<td width="209"><label>
<input name="total" type="text" id="total" size="32" disabled="disabled" value="0"/>
m 3/s</label></td>
</tr>
<tr>
<th><div align="right">Flow Depth, y =</div></th>
<td><label>
<input name="fd" type="text" id="fd" size="32" />
m ?</label></td>
</tr>
<tr>
<th><div align="right">Width of Channel =</div></th>
<td><label>
<input name="woc" type="text" id="woc" size="32" disabled="disabled" value="0" />
m</label></td>
</tr>

</table>```

2. The radio name is a collection, so reference as an array:
Code:
```// multiple names
for(var i=0; len=aRadio.length, i<len; i++) {
break;
}
}
// 2 names
var n = (document.SignupForm.n[0].checked)? document.SignupForm.n[0].value : document.SignupForm.n[1].value;```

3. Thanks, it works!!!

4. but how to retrieve 1 value only??

5. var "n" will have the value of the checked radio control; only one radio, using the same name, can be checked.
In your document you have 4 "n" radio's, only one can be checked.

I try use your code but still occur some problem

Code:
```// 2 names
var n = (document.SignupForm.n[0].checked)? document.SignupForm.n[0].value : document.SignupForm.n[1].value;```

7. You have 4 with name="n", not 2
Code:
```    <td><label>
<input type="radio" name="n"  value="0.030" onChange="MyCalc()" />
0.030</label></td>
<td><label>
<input type="radio" name="n" value="0.035" onChange="MyCalc()" />
</label>
0.035</td>
</tr>
<tr>
<th>Tall Grass Cover</th>
<td><label>
<input type="radio" name="n"  value="0.035" onChange="MyCalc()" />
0.035</label></td>
<td><label>
<input type="radio" name="n"  value="0.050" onChange="MyCalc()" />
0.050</label></td>```

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