We Keep Coding

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

Regex real number

I need real numbers in TextBox. I try my code online here
"^-{0,1}[0-9]{1,3},{0,1}[0-9]{1,2}$"
and its working perfectly, but in my project not working.
Please show me how I must do it

Would TryParse works for you? From MSDN:
Converts the string representation of a number in a specified style and culture-specific format to its double-precision floating-point number equivalent. A return value indicates whether the conversion succeeded or failed.
And for you, it could be something like this:
private void c_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
double num;
e.Handled = double.TryParse(e.Text, out num);
// if e.Text is a number, e.Handled will be true and num = e.Text
}

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.

Cannot implicitly convert type 'string' to 'int' where input can be numeric or alphanumeric.

I'm trying to make a masked Textbox that has a partial value already set and then the user needs to enter 4 more digits then allow it to send out. I've had a hard time trying to explain but here's what it currently looks like for reference:
private void maskedTextBox1_KeyDown(object sender, KeyEventArgs e)
{
if(e.KeyCode == Keys.Enter && maskedTextBox1.Text.Length == ("007744D4 0131").Length + 4)
{
NCInterface.ConstCodeAdd(codes[maskedTextBox1.Text], true);
}
}
Now the last part where it has NCInterface, is where it is being sent to the PS3 console, and where I need to know how to make sure that maskedTextBox1.Text converts properly. The maskedTextBox needs to be able to accept both numbers and letters. I have nothing to really compare this to.. But that's just where its sent from. But it just says that it cant convert type string to int. So if anyone is able to give me a hand it'd be much appreciated.

Just based on your error you might do this:
NCInterface.ConstCodeAdd(int.Parse(codes[maskedTextBox1.Text]), true);

What you need to do is use TryParse
string testString = maskedTextBox1.Text;
int numberTest;
if(int.TryParse(testString, out numberTest)
{
NCInterface.ConstCodeAdd(numberTest, true);
}

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);
}
}