How to calculate a formatted textbox in asp.net?

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I have a web form that has textboxes on it. I am using this format for the textboxes:

C#

TextBox1.Text = string.Format("{0:0,0}", double.Parse(TextBox1.Text));
TextBox2.Text = string.Format("{0:0,0}", double.Parse(TextBox2.Text));
TextBox3.Text = string.Format("{0:0,0}", double.Parse(TextBox3.Text));

I also have a Textbox textchange in place to do some calculations. When it is time for the calculations to do what it does the user gets this error:

HTML

Input string was not in a correct format.

Here is the calculation code for one of the textbox text change:

C#

protected void TextBox1_TextChanged(object sender, EventArgs e)
    {
        int i = Convert.ToInt32(TextBox1.Text);
        int j = 12;
        TextBox5.Text = Convert.ToString(i / j);
    }

How can I correct this error to do the calculations?

Posted 6-Oct-14 8:18am

Computer Wiz99

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Sergey Alexandrovich Kryukov 6-Oct-14 15:39pm

Why doing so?! Let's say, input text is "42". Then you will produce "42:42,42". Why? Did you ever here the concepts if informatics, such as entropy?
Besides, you repeat 3 identical lines of code. It should be a call to some method with text box reference used as a parameter. Repeating line of code is opposite to programming.

Also, avoid using convert in such cases. What you do is parsing, so use int.Parse, int.TryParse instead, and the like.

—SA

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Afzaal Ahmad Zeeshan · Answer 1 · 2014-10-06T08:28:00

Solution 1

Since you're parsing the string values to integer values (or double as in the String.Format() block). You need to know that 'a' cannot be converted to an integer. Whereas '0' can be.

What I mean is, that the string contains some characters that are not valid numbers. You need to make sure that the characters are numbers.

Quote:
Input string was not in a correct format.

Above statements tells it all, you need to make sure that the characters are actually numbers and can be converted to double or integers respectively.

On MSDN, a quick Google resulted in this link, http://msdn.microsoft.com/en-us/library/bb397679.aspx[^] where it has been made clear that while converting String to other formats like Integer, Double etc, you need to be carefull because String can contain alphanumeric content, whereas double, int, float are restricted to numbers only.

Only way to correct this, is to remove all of the characters from the textboxes that are not numbers, even whitespaces (use .Trim() on the string to remove extra spaces at start or end).

Since you're using ASP.NET, in ASP.NET there is a function used to determine whether the string is an int or not, you can use as

C#

if(variableName.IsInt()) {
   // yes, the variable has int values
   // parse them, convert them, use them
} else {
   // prompt for a valid data
}

You can try out many other ways, but remember, always use if else block to check for small conditions like this one.

Posted 6-Oct-14 8:28am

Afzaal Ahmad Zeeshan

Comments

Computer Wiz99 6-Oct-14 15:07pm

Afzaal Ahmad Zeehan, Thanks for the post. Where would I put the use.Trim() in my code to get just the numbers?

Afzaal Ahmad Zeeshan 6-Oct-14 15:13pm

.Trim() method is used on strings, to remove extra whitespaces at the start or end. Whereas the second method can be used by you to check whether it is a number or not. Make sure the user enters the numbers. It won't be a good idea to remove the content from the data user has provided.

Computer Wiz99 6-Oct-14 15:29pm

So do I put the .Trim() method on the calculation code or the formatted code?

Afzaal Ahmad Zeeshan 6-Oct-14 15:30pm

As I have already said, don't use Trim to remove alphabets. Use the IsInt() method in the if else block and use the parser inside it.

Computer Wiz99 6-Oct-14 15:34pm

Okay, I got the don't use .Trim() method. Can you show an example of the IsInt() method?

Afzaal Ahmad Zeeshan 6-Oct-14 15:38pm

Here: http://msdn.microsoft.com/en-us/library/system.web.webpages.stringextensions.isint(v=vs.111).aspx they've the document for it, since I am not having WebMatrix ready right away so I won't be able to provide an example to you. You can learn the IsInt() function from there. It is applied to the string, and returns true is the string can be converted to number. Otherwise false, to indicate there are invalid characters.

Sergey Alexandrovich Kryukov 6-Oct-14 15:41pm

The main point here: the whole idea of OP is something wrong. Please see my comment to the question.
More generally, this is a really bad idea to modify the user's input for formatting it (especially in this weird way).
—SA

Afzaal Ahmad Zeeshan 6-Oct-14 15:46pm

Exactly, I have also mentioned in my comments that converting the data provided by the user is not a good way of doing these things. He can just simply prompt the user to rewrite the input if the input is not a character. And as you've explained, the , might also cause a trouble here in the numeric parsing of the string.

Computer Wiz99 6-Oct-14 15:50pm

Okay, show me a code in C# where the textbox can auto input commas when the user enter numbers and it also does the calculations on different textboxes. I tried to use jQuery with no luck.

Afzaal Ahmad Zeeshan 6-Oct-14 15:56pm

For that the code would be changed, for example, when you want to print the data to the screen, you will be it like the one you're having in the String.Format() otherwise in the code behind, you will keep the pure integer values. This will lessen the errors of "Input string was not in a correct format." error too. You can always convert the results in any format. It is good to have the basic format, and then convert it whereever needed.

Computer Wiz99 6-Oct-14 16:02pm

I understand that part but show me what it will look like even if it has to be changed.

Afzaal Ahmad Zeeshan 6-Oct-14 16:04pm

Didn't you read the answer? See the code block in it.

Computer Wiz99 6-Oct-14 16:15pm

Okay, Thanks. I will try another way.