How to Cast String to Int. Error Msg: Input String Was Not in a Correct Format

Not able to cast string to int. Error msg: Input string was not in a correct format

I think the line "Input string was not in a correct format" explains it all. In the line

 int i = Convert.ToInt32(str);

str might be containing alphabetic characters. Take a look at it while debugging, what does it contain?

How do I handle input string was not in correct format

A System.FormatException happens when you want to "parse" a string to another type, like an integer, that makes a number in text be represented as a real number, in your case, you are calling Convert.ToInt32, be sure that whatever string being passed as argument to this method, don't overflow the capabilities of the Int32 struct, or that the text does not contain letters or decimal points. If that is the case, to verify if a number is valid use int.TryParse, it will only return true if the text is in a correct format like so:

if (int.TryParse("5", out int number))
{
    // Do something with that number
}

Here, if "5" is not a number, the if block will be completely skipped.

Input string was not in a correct format. Textchange problem

An empty string cannot be parsed as an int. As others have mentioned, you can use int.TryParse which accepts a string as the first parameter and an out int as the second parameter, which holds the parsed value. You could do this:

int overallTotal = 0;
int a = 0;
int b = 0;

// TryParse returns a bool
// If either of these fails, the variable a or b will keep the default 0 value
int.TryParse(txtSubtotal.Text, out a);
int.TryParse(txtAdvancePayment.Text, out b);

// Sum a and b
overallTotal = a + b;

If you want to show an error to the user that one or both fields isn't a valid integer, you can assign a bool variable such as var aIsNumber = int.TryParse(...) and then check if aIsNumber or bIsNumber is false. If so, then a and/or b could not be parsed to an int.

System.FormatException: Input string was not in a correct format from an int.Parse

int.Parse() will fail with that exception if the value you provide it is not capable of being converted to an int, and as written you have no checks on the string being read from the console to verify that is the case before passing it to the method.

You can use int.TryParse() instead, which gives you a bit more control over how to handle a failure by returning a boolean indicating success. You might present an error message instead, and ask the user to resubmit.

string input = Console.ReadLine();
int result;

if(int.TryParse(input, out result)) // TryParse returns a boolean showing whether the parse worked
{
   // then perform your behavior safely
}

VB.NET Convert String to Int throws error : Input String was not in a correct format

Try this :

Dim Total As Integer
Total = Integer.Parse(lblOldQty.Text) - Integer.Parse(txtQty.Text)
Dim Value As String = lblOldQty.Text + " - " + txtQty.Text + " = " + Convert.ToString(Total)
lblNewValue.Text = Value

Use breakpoint while execution and check if values are passing correctly to lblOldQty.Text and txtQty.Text

{Input string was not in a correct format.}

The documentation of Conver.ToInt32 tells us that the FormatException is thrown when:

value does not consist of an optional sign followed by a sequence of digits (0 through 9).

So basically your string can only have this format + or - followed by digits which are not allowed to be separated by a space or anything else but a digit.

ToInt32 is even so fair as it allows you to have a preceding or trailing space ;)

Edit:

The format is meant like this:

string input_pos = "+42"; // or
string input_neg = "-42";
Convert.ToInt32(input_pos) + Convert.ToInt32(input_neg);    
                           ^
                           |
                        //This has nothing to do with the format!

the format refers to the string that you pass as parameter into the ToInt32() method, and not how you calculate the resulting numbers!

Apparently you have a floating number in your array 3.49 this cannot be converted to an int but it can be converted into a double:

double tot = (Convert.ToDouble(a[4]) * Convert.ToDouble(a[5]));

the ToString() call is not necessary

Input string was not in a correct format

The error means that the string you're trying to parse an integer from doesn't actually contain a valid integer.

It's extremely unlikely that the text boxes will contain a valid integer immediately when the form is created - which is where you're getting the integer values. It would make much more sense to update a and b in the button click events (in the same way that you are in the constructor). Also, check out the Int.TryParse method - it's much easier to use if the string might not actually contain an integer - it doesn't throw an exception so it's easier to recover from.

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