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My regex match positive real numbers doesn't work

I am reading from a TextBox in C# and I want to make sure that only real positive values are allowed (including integers).
i.e. 1, 23, 23., 23.0, 23.42, etc.
The Regex I am using is:
[0-9]+\\.?[0-9]*
But C# does only let me type numbers and I can never put a period.
Thank you
Code:
private static readonly Regex rgx_onlyPositiveReals = new Regex("[0-9]+\\.?[0-9]*");
private void TextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
e.Handled = !IsSamplingRateAllowed(e.Text);
}
private static bool IsSamplingRateAllowed(string text)
{
if(rgx_onlyPositiveReals.IsMatch(text))
{
if(text.Equals(".") || float.Parse(text) <= 0.0)
{
MessageBox.Show("Sampling Rate has to be positive.", "Wrong Sampling Frequency Error", MessageBoxButton.OK, MessageBoxImage.Error);
return false;
}
return true;
}
return false;
}

From the looks of things this input box is supposed to only contain the number and no other text; in this case I would avoid the regular expression altogether.
Given that you're parsing the regex match result into a float anyway, it might make more sense to try parsing the input as a float directly which has the added benefits of allowing any valid positive float that can be parsed in the first place, it also allows entering the number in any other valid formats supported by float.Parse/float.TryParse e.g. scientific notation "1E5" == 100000f or commas "1,500" == 1500f (depending on the culture) without any additional effort.
private static bool IsSamplingRateAllowed(string text)
{
float number;
return float.TryParse(text, out number) && number >= 0.0f;
}
Unless this data is being used for some external process as a string with additional restrictions on the format (which seems unlikely and is worth including in the question if that is the case), then if it isn't already, I'd recommend separating this input box from any other information and have users enter the number and only the number directly into the box. If you need to collect other information from the user you can add other input boxes and controls as necessary (which can also simplify validation for other pieces of information).

Give this a try
The pattern is ^[0-9]+\.?[0-9]*
In C# you can prefix your string with # which makes it easier to read a regex. It results in the following:
"\\this \\is \\the \\same" == #"\this \is \the \same"

You can simply use the below Regex
^\d*[.]?\d*$
Demo Fiddle

Issue with Validating Phone number on user input,Int to large c#

Overview of Project:
I am creating a multi form application, which consist of two forms and one parent class. Both Forms have a series of validation functions, such as isLetter() isNumber() and isValidEmail(). My Issue comes when using the isNumber() Function.
public static bool numValidation(string strNum)
{
if (!string.IsNullOrWhiteSpace(strNum))
{
int temp;
if (int.TryParse(strNum, out temp))
{
Console.WriteLine("Phone Number is a valid input: " + temp);
return true;
}
else
{ Console.WriteLine(temp + "Is not Valid input!!"); }
}
return false;
}
At first glance it works fine but once I tried to break it, I realised that when an actual phone number is entered I get an error saying that the number is too high. Any ideas how to get round this constraint ? as the only reason I need this validation is for phone numbers, Fax etc. I simply need this function to accept very large numbers such as phone numbers

I suggest that you use a regular expresion to validate the input in your case
public static bool numValidation(string strNum)
{
Regex regex = new Regex(#"^[0-9]+$");
return (regex.IsMatch(strNum)) ;
}
Parsing a string and not using that value is not really needed.
For more details checkout this answers - Regex for numbers only

From Mauricio Gracia Gutierrez answer
I suggest that you use a regular expresion to validate the
input in your case
public static bool numValidation(string strNum) {
Regex regex = new Regex(#"^[0-9]+$");
return (regex.IsMatch(strNum)) ; } Parsing a string and not using that value is not really needed.
For more details checkout this answers - Regex for numbers only
You could enhance the expression to check the length of the number:
Between 5 and 10 digits:
Regex regex = new Regex(#"^[\d]{5,10}+$");
Max 10 digits:
Regex regex = new Regex(#"^[\d]{10}+$");
At least 5 digits:
Regex regex = new Regex(#"^[\d]{5,}+$");

Basic Regex help needed

I'm really new to programming and haven't come across Regex until now, I am looking to restrict textbox input to double class values only and came across this:
`Regex regex = new Regex("[^0-9-]+");
TextP1_TextChanged = regex.IsMatch(TextP1.Text);`
I want to implement into my program and am assuming it occurs under the TextChanged event, but I don't actually have the knowledge to implement regex and so am just looking for any help.
Update
I've implemented TryParse but am looking to accept decimal numbers with or without 0 in front, i.e. 0.234 or .234. My new code is this:
private void TextP1_TextChanged(object sender, EventArgs e)
{
bool isDouble = Double.TryParse(TextP1.Text, out P1);
if(isDouble == false)
{
MessageBox.Show("Text box only accepts positive number values", "Text entered into P1 is invalid", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
}

You could use this regular expression [0-9]*\.[0-9]*. The * means 0-9 can occur 0 to x times.
You could use regexr to test regular expression in a fast way.

TextBox Validation - C#

I am having quite a hard time with my C# Application's textbox validation. The thing is, the said textbox should only accept decimal values. so it means, there should be no letters or any other symbols aside from the '.' symbol. The letter filter, i can handle. However, i don't exactly know how I can manage to filter the number of '.' that the textbox should accept. If anybody has any idea how to do this, please give me an idea.
Thank you very much :)

decimal value;
bool isValid = decimal.TryParse(textBox.Text, out value);
if (!isValid)
{
throw new ArgumentException("Input must be a decimal value");
}

this should work!!!
modified for just one decimal
private void txtType_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.Back || (e.KeyChar == (char)'.') && !(sender as TextBox).Text.Contains("."))
{
return;
}
decimal isNumber = 0;
e.Handled = !decimal.TryParse(e.KeyChar.ToString(), out isNumber);
}

Use regex validation:
^([0-9]*|\d*\.\d{1}?\d*)$
This site has a library of regex validation (including numeric related) that you'll find useful:
http://regexlib.com/Search.aspx?k=decimal&c=-1&m=-1&ps=20

Just a thought: if you are monitoring the decimal places, simply keep a bool flag in your control to say "I've already had a dot"; subsequent dots are invalid.
Alternatively, when checking for decimal places, you can use Contains:
if (textbox.Text.Contains("."))
Also, review this sample available on MSDN (NumericTextBox):
http://msdn.microsoft.com/en-us/library/ms229644(VS.80).aspx

Use a MaskedTextBox instead and set the mask to only accept decimals.

Allow user to only input text?

how do I make a boolean statement to only allow text? I have this code for only allowing the user to input numbers but ca'nt figure out how to do text.
bool Dest = double.TryParse(this.xTripDestinationTextBox.Text, out Miles);
bool MilesGal = double.TryParse(this.xTripMpgTextBox.Text, out Mpg);
bool PriceGal = double.TryParse(this.xTripPricepgTextBox.Text, out Price);

Update: looking at your comment I would advise you to read this article:
User Input Validation in Windows Forms
Original answer: The simplest way, at least if you are using .NET 3.5, is to use LINQ:
bool isAllLetters = s.All(c => char.IsLetter(c));
In older .NET versions you can create a method to do this for you:
bool isAllLetters(string s)
{
foreach (char c in s)
{
if (!char.IsLetter(c))
{
return false;
}
}
return true;
}
You can also use a regular expression. If you want to allow any letter as defined in Unicode then you can use this regular expression:
bool isOnlyLetters = Regex.IsMatch(s, #"^\p{L}+$");
If you want to restrict to A-Z then you can use this:
bool isOnlyLetters = Regex.IsMatch(s, #"^[a-zA-Z]+$");

You can use following code in the KeyPress event:
if (!char.IsLetter(e.KeyChar)) {
e.Handled = true;
}

You can use regular expression, browse here: http://regexlib.com/

You can do one of a few things.
User Regular Expression to check that the string matches your concept of 'Text' only
Write some code that checks each character against a list of valid characters. Or even use char.IsLetter()
Use the MaskedTextBox and set a custom mask to limit input to text only characters

I found hooking up into the text changed event of a textbox and accepting/rejecting the changes an acceptable solution. To "only allow text" is a rather vague definition, but you may as well check if your newly added text (the next char) is a number or not and simply reject all numbers/disallowed characters. This will make users feel they can only enter characters and special characters (like dots, question marks etc.).
private void UTextBox_TextChanged(object sender, EventArgs e)
{
string lastCharacter = this.Text[this.Text.Length-1].ToString();
MatchCollection matches = Regex.Matches(lastCharacter, "[0-9]", RegexOptions.None);
if (matches.Count > 0) //character is a number, reject it.
{
this.Text = Text.Substring(0, Text.Length-1);
}
}