how to accept a float value in textbox?

Use Compare validator

<asp:textbox id="textbox11" runat="server" xmlns:asp="#unknown"></asp:textbox>
<asp:comparevalidator id="intValidator" runat="server" controltovalidate="textbox1" operator="DataTypeCheck" type="float" errormessage="Value must be float" xmlns:asp="#unknown" />

put one regular expression in front of that textbox and control that text box which ever it is.
goto properties and do this....
validate expression: ^([0-9].[0-9])*$

1. Are you using WinForms or ASP.NET ?

2. Do the float values have a fixed format: i.e., are there always going to be the same number of digits before the decimal point ?

Use of a MaskedTextBox is not indicated when the format of input varies, like the number of digits before the decimal point.

Another strategy is to intercept the keystrokes being put into a TextBox as they are typed, and limit them to only digits and the decimal point.

And, as one answer points out here: if you want to let the user type anything and check later, validation can be done, using a RegEx.

You need to specify more clearly what your question is.

If you are using asp.net, Use compare validator

<asp:CompareValidator ID="CompareValidator1" runat="server"ControlToValidate="TextBox1" ErrorMessage="Value must be double";CompareValidator"style="top: 70px; left: 418px; position: absolute; height: 19px; width: 113px"Type="Double"></asp:CompareValidator>

If you are using windows form, handle the KeyPress event of the TextBox
for numeric values only.