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Input string was not in a correct format in a Formula

I was try to create a formula that will calculate the total amount and show it in a textbox , but there's an error that says
" Input string was not in a correct format."
private void txtQUANTITYPOS_TextChanged(object sender, EventArgs e)
{
txtTOTALPOS.Text = (Convert.ToDouble(txtPricePOS.Text) * Convert.ToDouble(txtQUANTITYPOS.Text)).ToString();
}
Can you help me please , thank you again in advance :)

One possible scenario - You may have enter a number in your txtQUANTITYPOS textbox but txtPricePOS textbox is still empty. Therefore, you probably getting this error because your txtPricePOS textbox doesn't contains a number yet.
You could use Double.TryParse instead to ensure your are not multiplying other character rather than numbers:
Following an example of how you could implement it:
private void txtQUANTITYPOS_TextChanged(object sender, EventArgs e)
{
double pricePos;
double qtyPos;
if (!double.TryParse(txtPricePOS.Text, out pricePos))
return; // Will return in case txtPricePOS.Text is not a number
if (!double.TryParse(txtQUANTITYPOS.Text, out qtyPos))
return; // Will return in case txtPricePOS.Text is not a number
txtTOTALPOS.Text = (pricePos * qtyPos).ToString();
}

Format error clearing TextBox parsed as integer

I am using Windows Form Application and am having an issue clearing a user textbox. The textbox is getting parsed as an int. I have a button near the bottom of the app that allows a user to clear different parts of the form, labels textboxes etc.
The labels clear fine but any textbox that has been parsed to int I get error on the TextChanged method.
xxx = textbox name
yyy = new int var used in other parts of code
when xxx.Clear(); is called I get exception below:
An unhandled exception of type
System.FormatException' occurred in mscorlib.dll
Additional information: Input string was not in a correct format.
Here is example of code
private void xxx_TextChanged(object sender, EventArgs e){
// parse user text and convert to int
yyy = int.Parse(xxx.Text);
}
private void btnExit_Click(object sender, EventArgs e){
// close program
this.Close();
}
private void btnClear_Click(object sender, EventArgs e){
xxx.Clear();
}

put the textBoxName.Text in a variable and check if its value is null or not.
int xxx = textbox.Text ;
if(xxx == ""){
//do something
}

well when you use int32.parse you should be carefull that your string be not null and all contain numbers like
"123456789"
if you think you string might be null ot contain not number characters you should use:
int32.TryParse(string String, out int iString);
and use it like this:
int i = 0; // default
string s = "somthing123somthing456blah";
int32.TryParse(s, out i);
result should be: 123456 as integer
EDIT:
if you dont what TextChanged fire:
mytextbox.TextChanged -= myTextBox_TextChanged;
make you change and:
mytextbox.TextChanged += myTextBox_TextChanged;

I suspect something to do with code re-entry. When xxxTxtBox.Clear() is called, the TextChanged method is called, meaning int.parse is called on an empty textbox (null or string.empty can't be parsed to an integer), throwing an exception.
A preferred way to fix that may be setting a flag upon re-entry, something like this.
The easy way is put your TextChanged() logic in a try/catch, meaning that upon re-entry, the int.parse() fails but your user doesn't see a problem.

You need evaluate if the textbox is empty:
enter private void xxx_TextChanged(object sender, EventArgs e)
{
// parse user text and convert to int if value is't Empty
yyy = String.IsNullOrEmpty(xxx.Text) ? 0 : int.Parse(xxx.Text);
}
And try this:
private void btnClear_Click(object sender, EventArgs e){
xxx.Text = String.Empty;
}

To clarify, as some others have pointed out, the problem you are experiencing is due to the fact that xxx_TextChanged() is being called when xxx.Clear() is called and the textbox content changes to an empty string. This causes int.Parse() to execute against an empty string, which produces said error.
To circumvent this problem, you should change the xxx_TextChanged() method to something similar to as follows:
private void xxx_TextChanged(object sender, EventArgs e)
{
// Parse user text and convert to integer, when able:
if ((string.IsNullOrEmpty(xxx.Text)) ||
(!int.TryParse(xxx.Text, out yyy)))
{
yyy = 0;
}
}
Notice the key difference is the "null or empty" check against the text box contents. There is no need to parse a null value or an empty string. Also, instead of using int.Parse(), we can use the int.TryParse() method so that invalid numeric input (e.g., "abc") does not produce an error, but instead is assigned some default value (in this case, 0).
The rest of the code can remain as-is.

How to set TextBox to only accept numbers?

I have already checked other questions here but the answers are not related to my issue. the following code allows textbox1 to only accept numbers if the physical keyboard (laptop) is pressed:
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
char ch = e.KeyChar;
if ( !char.IsDigit(ch))
{
e.Handled = true;
}
}
but this is not what I wanted (I dont use physical laptop keyboard).
As shown in screenshot, I have windows form with buttons and a textbox. I designed this keyboard and it works well but I want textbox1 to only accept numbers and the ".".
There are only two lines of code inside each button (and only code in the project) which is:
private void buttonName_Click(object sender, EventArgs e)
{
// each button only has this code.
textBox1.Focus();
SendKeys.Send(buttonName.Text);
}
I know how to set txtbox to accept numbers if the physical (laptop ) keys are pressed but here in this case I have control buttons in windwos form and I want to set textBox1 to only accept numbers and the ".". Please help in how to achieve this. Thank you

Declare a string variable at form level, use it to store the last valid text and to restore it when an invalid text is entered on the TextChanged event of your textbox.
string previousText;
public Form1()
{
InitializeComponent();
previousText = String.Empty;
}
private void textBox1_TextChanged(object sender, EventArgs e)
{
int dummy, changeLenght, position;
if (!String.IsNullOrWhiteSpace(textBox1.Text) && !int.TryParse(textBox1.Text, out dummy))
{
position = textBox1.SelectionStart;
changeLenght = textBox1.TextLength - previousText.Length;
textBox1.Text = previousText;
textBox1.SelectionStart = position - changeLenght;
}
else
{
previousText = textBox1.Text;
}
}
position and changeLenght are used to keep the cursor where it was before restoring the text.
In case you want to accept numbers with decimals or something bigger than 2147483647, just change dummy to double and use double.TryParse instead of int.TryParse.
private void textBox1_TextChanged(object sender, EventArgs e)
{
int changeLenght, position;
double dummy;
if (!String.IsNullOrWhiteSpace(textBox1.Text) && !double.TryParse(textBox1.Text, out dummy))
{
...
}
}

Suppose button1 is your button control, you could do this:
private void allButtons_Click(object sender, EventArgs e)
{
Button btn = sender as Button;
char c = btn.Text[0]; //assuming all buttons have exactly 1 character
if(Char.IsDigit(c) || c == '.')
{
//process
textBox1.Focus();
SendKeys.Send(btn.Text);
}
//otherwise don't
}
I'm assuming you put this in a common handler, to which you already wired all your buttons (i.e. allButtons_Click).
Problem with this approach, it allows you to type values like 0.0.1, which are most likely invalid in your context. Another way to handle this is to process TextChanged event, store previous value, and if new value is invalid, restore the old one. Unfortunately, TextBox class does not have TextChanging event, which could be a cleaner option.
The benefit of you determining the invalid value is modularity. For example, if you later decide your user can enter any value, but only numbers can pass validation, you could move your check from TextChanged to Validate button click or similar.
Why users may want that - suppose one of the options for input is copy/paste - they want to paste invalid data and edit it to become valid, for example abc123.5. If you limit them at the entry, this value will not be there at all, so they now need to manually paste into Notepad, cut out in the invalid characters, and paste again, which goes against productivity.
Generally, before implementing any user interface limitation, read "I won't allow my user to...", think well, whether it's justified enough. More often than not, you don't need to limit the user, even for the good purpose of keeping your DB valid etc. If possible, never put a concrete wall in front of them, you just need to guide them correctly through your workflow. You want users on your side, not against you.

C# Conversion throwing exceptions

So, I'm working in C# and for some reason my conversion is throwing exceptions, the code is meant to execute when user presses a button, here is the code.
private void tbVerk6Breidd_KeyDown(object sender, KeyEventArgs e)
{
int width = Convert.ToInt32(tbTextBox.Text); //Crashes here
}
Any help appreciated :)
Edit
Heki mentioned that KeyUp would be a better idea, that worked. Thanks :)
private void tbVerk6Breidd_KeyUp(object sender, KeyEventArgs e)
{
int width = Convert.ToInt32(tbTextBox.Text);
}

if you don't know if the textbox is filled or contains not numerical value, try:
private void tbVerk6Breidd_KeyDown(object sender, KeyEventArgs e)
{
int width;
int.TryParse(tbTextBox.Text, out width )
}
if the text input is not a convertible integer you will retrieve 0

Convert.ToInt32(tbTextBox.Text) can throw two type of exception.
1. FormatException // let say tbTextBox.Text = "abcdefghijkl";
2. OverflowException // let say tbTextBox.Text = "12345890690123456789012345997890";
so check what parameter do you have in tbTextBox.Text.
Solution: As mentioned above use 'TryParse' method of int.
Further read : -https://unwrapdotnet.wordpress.com/2014/01/14/all-about-int32-parse-convert-toint32-int32-tryparse/

The Convert.ToInt32 methods throws two possible exceptions:
FormatException
value does not consist of an optional sign followed by a sequence of digits (0 through 9).
OverflowException
value represents a number that is less than Int32.MinValue or greater than Int32.MaxValue.
I guess you get a FormatException because the string within the textbox does not represent a valid int.
In your question you wrote ...the code is meant to execute when user presses a button, here is the code.. But you event handler is registred for a KeyDown event? If you want to check when ever the text within the text box changes (regardless of by copy paste or keyboard interaction) I recommend to use the TextChanged event of the textbox.
private void tbVerk6Breidd_TextChanged(object sender, EventArgs e)
{
int parsed;
if (int.TryParse(tbTextBox.Text, out parsed))
{
// parsed successfully
}
else
{
// invalid value
}
}

try
{
int width = int.Parse( tbTextBox.Text);
// do what you want to do
}
catch
{
// do nothing, log?, display an error message ( that would probably be annoying )
}
You might also want to use a numeric up down control.
https://msdn.microsoft.com/en-us/library/system.windows.forms.numericupdown(v=vs.110).aspx
I don't know if you want to differentiate between the user actually entering "0", which is a valid input, and the case where they entered invalid data like "abasr4ra".

Using Show() to display data from another class

I know how to create programs in C++, but very new to C# so be patient, but I have a question, and for the life of my couldn't find it on google, or stackoverflow search (maybe didn't know a good way to phrase it). I have two functions on my form: A NumericUpDown, and a Button. When the button is clicked, I want to grab the data from NumericUpDown, and .Show() it in a message box. Here is what I currently have.
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void StatBox_ValueChanged(object sender, EventArgs e)
{
//decimal Stat = StatBox.Value;
//string StatStr = Stat.ToString();
}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show(StatBox.Value);
}
}

Like C++, C# is a strongly-typed language. That means that you will get a compile-time error if you try to pass an int to a function that accepts a string, or vice versa. That's what is happening to you here.
The simplest overload of the MessageBox.Show function accepts a single string parameter, yet you've passed it a decimal (the result of StatBox.Value):
MessageBox.Show(StatBox.Value);
The fix is simple: convert the decimal to a string. All .NET objects provide a ToString member function that can be used to obtain a string representation of the object. So rewrite your code like so:
MessageBox.Show(StatBox.Value.ToString());
You can even get fancy and concatenate a number of sub-strings together when calling this function, just like you can with the C++ string type and I/O streams. For instance, you might write this code:
MessageBox.Show("The result is: " + StatBox.Value.ToString());
or use the String.Format method, which is somewhat similar to the C printf function. Then you can specify a standard or custom numeric format and avoid calling the ToString function explicitly. For example, the following code will display the number in the up-down control in fixed-point notation with exactly two decimal places:
MessageBox.Show(String.Format("The result is: {0:F2}", StatBox.Value.ToString()));

This should do it for you:
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void StatBox_ValueChanged(object sender, EventArgs e)
{
//decimal Stat = StatBox.Value;
//string StatStr = Stat.ToString();
}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show(StatBox.Value.ToString());
}
}
Since you are using a MessageBox to .Show() the data, you will want to call the .ToString() method on the StatBox.Value.
PS - Welcome to SO! You will love it here.