<div>
Not sure if this is something you want to update, but you could use a Masked Textbox with a mask of 0.0 
I believe that will only allow numbers in place of the zero's and would make it so it was only one place decimal wise. &nbsp;
</div>

<div>
If it is asp.net maybe you could consider the Ajax Tookit Masked Textbox: 
<a href="http://www.asp.net/AJAX/AjaxControlToolkit/Samples/MaskedEdit/MaskedEdit.aspx" rel="ugc">http://www.asp.net/AJAX/AjaxControlToolkit/Samples/MaskedEdit/MaskedEdit.aspx</a> 
&nbsp; 

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I have to do it in server side! &nbsp;VC# 
 
Yes, asp.net 
 

</div>

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Do they have to have exactly 1 decimal or can they have none eg: 
33.5 
or 36 

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<div>
{ 
&nbsp; &nbsp; string temp = null; 
&nbsp; &nbsp; temp = TextBox1.Text; 
&nbsp; &nbsp; int dotPos = 0; 
&nbsp; &nbsp; dotPos = temp.IndexOf(&quot;.&quot;); 
&nbsp; &nbsp; temp = temp.Substring(0, dotPos + 2); 
} 
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That doesn't check for all cases...but that should give you an idea if there is a decimal. &nbsp;You would have to add code to check for all possibles before that...
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<div>
Do they have to have exactly 1 decimal or can they have none eg: 
 
33.5 
 
or 36 
 
YES
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<div>
Ok check this out 
This checks it is a number too. 
&nbsp; 
 

<pre><code class="code-10 nolinks" id="code-262035">using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace EEConsoleApp
{
 class ValidateNumber
 {
 public static void Main()
 {
 Console.WriteLine(CheckNumber(&quot;22&quot;));
 Console.WriteLine(CheckNumber(&quot;22.3&quot;));
 Console.WriteLine(CheckNumber(&quot;22.44&quot;));
 Console.WriteLine(CheckNumber(&quot;22.1&quot;));
 Console.WriteLine(CheckNumber(&quot;22x&quot;));
 Console.WriteLine(CheckNumber(&quot;22.&quot;));
 
 Console.Read();
 }
 
 public static bool CheckNumber(string numberToCheck)
 {
 bool isValid = true;
 
 float result;
 
 if (!float.TryParse(numberToCheck, out result))
 {
 isValid = false;
 }
 else if (numberToCheck.Substring(numberToCheck.Length - 2, 1) != &quot;.&quot;)
 {
 isValid = false;
 }
 
 return isValid;
 }
 }
}
</code></pre>
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<div>
Yes? 
That was an either or question eg is it a or b. 
You cannoy answer yes to an either or question! 
Do they have to have exactly 1 decimal OR can they have no decimals as well? 

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<div>
sorry 
need both 
 
33.5 and 36 
 
YES
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<div class="content wysiwyg-content">
Hi 
 
I have a textbox let user input decimal numbers 
 
e.g. 123.45 
330.7 
66.987 
 
However, I want to limit it to be one decimal place for all input. 
 
so, they become 
123.4 
330.7 
66.9 
 
How can I do it in C# server side? 
 
substring() how should use it?
</div>
</div>

Hi

I have a textbox let user input decimal numbers

e.g. 123.45
330.7
66.987

However, I want to limit it to be one decimal place for all input. 

so, they become
123.4
330.7
66.9

How can I do it in C# server side? 

substring() how should use it?

How to substring only one decimal place number?

The .NET Framework is not specific to any one programming language; rather, it includes a library of functions that allows developers to rapidly build applications. Several supported languages include C#, VB.NET, C++ or ASP.NET.