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How do I make a richtextbox limited to only digits with a max number? (Cap)

Hey guys I wanted to make a richtextbox that only supports numbers and cant go above, 500 for example.
how would I go by doing that? thanks

I would use the keydown event to check if the pressed key is one of the keys you allow. With numbers it is pretty simple, maybe add ',' and '.' or other characters of your choice.

I'm not sure about the specifics but you can add something like
myRichTextBox.OnTextChanged() {
int number = 0;
bool checkInt = Int32.TryParse(myRichTextBox.Text, out number); //this checks if the value is int and stores as true or false, it stores the integer value in variable "number"
if ( checkInt = true && number > 500 ) //check if value in textbox is integer
{
myRichTextBox.Text = number.ToString();
}
else
{
DialogBox.Show("Please Enter Numbers Only");
myRichTextBox.Text = "";
}
}
You probably have to read the Int32.TryParse usage but brushing up this code should do what you want.
You can also put this code in a button onclick method to check that the value in textbox is integer before using the text.

Converting String to Double from ListBox to TextBox

// Calculating and diplaying pricing in list.
for (double MAX = 4.25; MAX >= MIN; MAX -= 0.05)
{
Price = (X * MAX);
prices = Price.ToString("c");
listFinances.Items.Add(prices);
}
---
private void listFinances_SelectedIndexChanged(object sender, EventArgs e)
{
string TotalPrice = listFinances.SelectedItem.ToString();
double stateIncentive = (Convert.ToDouble(TotalPrice) / 4);
txtStateTax.Text = stateIncentive.ToString();
}
So I'm trying to take a ListBox of string currency values, turn them into a double, divide them by 4, and display the result in a TextBox. The user will select the ListBox value and the program should automatically divide by 4 and display.
It's not working however. The program always does an exception throw when you click the ListBox item. The exception is thrown at:
double stateIncentive = (Convert.ToDouble(TPrice) / 4);
saying that:
It's not in the correct format.
Can someone help me out here?

You add your strings with the currency symbol. If you want to parse the string back to a double (but it is better use a decimal) you need to tell the conversion that you have that symbol and ignore it
private void listFinances_SelectedIndexChanged(object sender, EventArgs e)
{
string TotalPrice = listFinances.SelectedItem.ToString();
decimal stateIncentive = decimal.Parse(TotalPrice, NumberStyles.Currency, CultureInfo.CurrentCulture) / 4);
txtStateTax.Text = stateIncentive.ToString();
}
I have used decimal instead of double because the decimal type is more adapt to handle money values. I suggest to make the same change in the for..loop that fill the list (Just use the suffix m to specify constant decimal values (IE. 4.25m and 0.05m)

You are trying to convert a currency string to double so you should Try like this:
double stateIncentive = (Double.Parse(TotalPrice, System.Globalization.NumberStyles.Currency) / 4);
Or would be better if using decimal (Read this to know why):
decimal stateIncentive = (decimal.Parse(TotalPrice, System.Globalization.NumberStyles.Currency) / 4);
The style parameter defines the style elements (such as white space, thousands separators, and currency symbols) refer to MSDN:Double.Parse Method (String, NumberStyles)

Round off in listview

I am trying to round off each row to the nearest 1.0 in a column of a listview, so meaning 1.58 should show 2.00 and 1.48 should be 1.00 -
Math.Round(listView1.Columns[2].ToString(), 10);

You need to use 0 in digits parameter. You expect no digits here, but you're passing 10 to digit parameter which says to round with 10 digits after decimal.
var res = Math.Round(1.58, 0);//2
var res = Math.Round(1.48, 0);//1
Just saw you try to Round the string, You'll have to convert it to Double or decimal or whatever.
var rounded = Math.Round(Double.Parse(listView1.Columns[2].ToString()), 0);

In case you want to get String as a final result (as far as you've put ToString() in your code), you may just use appropriate formatting string ("F0" in your case):
String result = (1.58).ToString("F0"); // <- "2"
...
String result = (1.48).ToString("F0"); // <- "1"

You can't round a string directly.
string val=listView1.Columns[2].ToString();
double i;
if(Double.TryParse(val, out i))
{
Console.WriteLine(Math.Round(i)); // you can use Math.Round without second
// argument if you need rounding to the
// nearest unit
}

Digit grouping with two decimal places in c#

I want to display a number which is of double datatype in C#, in grouped digits and with two decimal places only if it contains a decimal no.
e.g. If there is 2000.4567 and 2000.45, it must be displayed as 2,000.45 and if it is 2000 then it will displayed as 2,000 (grouped but without decimal).
I have tried this and it is working fine for digit grouping but it rounds off the decimal no. to an integer value either by floor or ceil:
DimensionLength.ToString("#,##0")
DimensionLength is of type double.

Try this Code
double s=123.345345;
string str=string.Empty;
str = s.ToString("#,0.##");
MessageBox.Show(str);

I think you are better off by creating your own custom condition
double _inputval=2000.4567
string _outputVal="";
if ((_inputval % 1) == 0)
{
_outputVal = _inputval.ToString("#,##");
}
else
{
_outputVal = _inputval.ToString("N2");
}
Hope it helps

How to convert maskedtextbox value to int if it's empty?

I am building this C# windows application. On a certain Form, I am using maskedtextbox to enter upto 3 numerical digits, then I convert it into int as I have to send all these data to database with an insert query, but the problem is that these maskedtextboxes give error when left empty:
int scd_user_comm = Convert.ToInt32(maskedTextBox1.Text);
and the error is :
Input string was not in a correct format.
The corresponding field in database allows null, so if left empty, it must not give an error. Can anyone help please?
One side question:: Can I use a textbox or maskedtextbox to ensure that user only enters numeric value b/w 0 to 100? Thanks in advance.

You could try the Int32.TryParse() method
int scd_user_comm;
if(Int32.TryParse(maskedTextBox1.Text, out scd_user_comm) == false)
scd_user_comm = 0;
this will give you all the flexiblity required to work with your integer var and your maschedTextBox-
To force your maskTextBox to accept only numeric values set
maskTextBox1.Mask = "999";
maskTextBox1.TextMaskFormat = MaskFormat.ExludePromptAndLiterals;
However this is not enough to ensure the enterd number is between 0 and 100.
To get this result you need to use the Validating event and reject the input if is outside your limits
private void maskedTextBox1_Validating(object sender, CancelEventArgs e)
{
int num;
if (Int32.TryParse(maskedTextBox1.Text, out num) == true)
{
if (num < 0 || num > 100)
{
MessageBox.Show("Insert number between 0 and 100");
e.Cancel = true;
}
}
}

You could use the TryParse instead:
int scd_user_comm;
if(!Int32.TryParse(maskedTextBox1.Text, out scd_user_comm))
{
// Do something to notify the user that the text isn't a number.
}