How can I convert a textbox into a float only when the textbox has value?
I currently have this float test = (float)Convert.ToDouble(textbox.Text);
It works fine, But gives an error if the textbox is empty.
I think that better solution will be:
float test = float.NaN;
if(float.TryParse(textbox.Text, out test ))
{
// your code here
}
There are many ways to do this, but generally you test with an if. For example:
float test;
if (!string.IsNullOrWhiteSpace(textbox.text))
test = (float)Convert.ToDouble(textbox.Text);
It really is as simple as including this in an If statement.
float test;
if(textbox.Text.Length > 0) //Or (textbox.Text != "")
test = (float)Convert.ToDouble(textbox.Text);
As an additional suggestion, multiple layers of validation is always a good thing. If you have something like a submit button, you should test against required fields being empty on the UI BEFORE it gets to the point where it is converted.
A very common way is to use double.TryParse to do the conversion. This way you can handle empty and invalid values with a single statement.
bool success = double.TryParse(textbox.Text, out value);
Don't forget to check success and handle a possible failure.
Related
I've been struggling to get my head around a natural way of using TryParse because I keep expecting it to work the other way around (i.e. to return the parsed value and emit the boolean for whether the input parsed).
For example, if we take a basic implementation of Parse, the return value is the parsed input:
int parsedValue = int.Parse(input);
This works fine until it gets a value that it can't parse, at which point it entirely reasonably throws an exception. To me, the option then is either to wrap the parse in something like a try-catch block to handle the exception and a condition to set a default, or just to use TryParse to let C# do all that for me. Except that's not how TryParse works. The above example now looks like this:
bool parseSucceeded = int.TryParse(input, out int parsedValue);
To get it to assign in the same way as Parse, I wrap it in a ternary conditional with parsedValue and a default value (in this case, 0) as the true and false results respectively:
int parsedValue = int.TryParse(input, out parsedValue) ? parsedValue : 0;
But I still feel like I'm missing the point with TryParse if I'm just working around its default behaviour like this. I've read Tim Schmelter's excellent answer in which he shows its internal workings, from which I can suppose that it returns the boolean because it's easier internally than passing it out at all the various places that it currently returns. But I'm not sure about this, and I'm not satisfied that I understand its intent correctly. I also tried reading the documentation for it, but the remarks don't clear up my confusion (I don't think they even make its differences with Parse clear enough, like the change in return type).
Am I understanding it correctly, or am I missing something?
Sure, it could have been implemented as
int TryParse(string input, out bool succeeded)
{
}
But as mentioned in a comment, the common use case for the function is:
string input;
int parsedValue;
if(int.TryParse(input, out parsedValue))
{
// use parsedValue here
}
With the signature you propose, that code would now be:
string input;
bool succeeded;
int parsedValue = int.TryParse(input, out succeeded)
if(succeeded)
{
// use parsedValue here
}
So there's more code for no functional benefit. Also, with your ternary operator, if the parse fails you just set a value of zero, which is unnecessary since the default value of it is 0. You could just do:
int parsedValue;
int.TryParse(input, out parsedValue);
If the parse fails, parsedValue will have a value of 0; (I also question if/how you distinguish between an actual result of 0 and a failed parse, but I'm sure you have a reason).
So there's no technical reason why the signature is the way it is; it's a design decision that is appropriate for the most common use cases.
Of course, now with tuples in C# 7 you could have:
(int parsedValue, bool succeeded) = int.TryParse(input);
but again there's little functional benefit and prevents you from inlining the TryParse in an if statement.
Because logically you would want to check that the TryParse succeeded before trying to use the out value.
So this is more concise:
if (int.TryParse(input, out int parsedValue)}
{
// Do something with parsedValue
}
Than this:
int parsedValue = int.TryParse(input, out bool succeded);
if (succeeded)
{
// Do something with parsedValue
}
I think, a large part of your confusion stems from the method name isn't named exactly right:
int parsedValue = int.Parse("42");
This makes perfect sense, give me the integeger representation of a string.
int parsedValue = int.TryParse(input);
This makes sense as an extension of the concept: Input might be '42' or 'Oswald', but if it's a number I want that number.
In 2020, I think a better name would be CanParse(string input, out int result).
It better matches style guides and naming conventions, where returning a bool should be named with Is, Has, or Can.
It better matches how we use TryParse 99% of the time:
if (int.CanParse(input, out int result))
{
return result * 10;
}
But where I feel the current name makes sense, is the problem I assume it was trying to solve: To get rid of the following boilerplate code:
int result;
bool hasValidNumber = false;
try
{
result = int.Parse(input);
hasValidNumber = true;
}
catch
{
// swallow this exception
}
if (hasValidNumber)
{
// do things with result
}
else
{
// use a default or other logic
}
need help to resolve this error please can someone correct this up? i've commented the line in below code
discount = Conversion.Val(Dt.Rows[indx]["DiscountRate"]);
subtotal = (int) ((days * rate) - ((days * rate) * discount));
*total = System.Convert.ToInt32(((Conversion.Val(subtotal.ToString()) - Conversion.Val(Dt.Rows[indx]["AdvancePayment"].ToString())).ToString("00.00")));*//Input string was not in a correct format.
if (Conversion.Val(subtotal.ToString()) > Conversion.Val(Dt.Rows[indx]["AdvancePayment"]))
{
lv.SubItems.Add(System.Convert.ToString(Conversion.Val(total.ToString())));
}
else
{
lv.SubItems.Add("0");
}
lvlcheckin.Items.Add(lv);
}
rs.Dispose();
Module1.con.Close();
You are formatting the double using ToString("00.00") you cannot convert this string to an Int32...
Console.WriteLine(System.Convert.ToInt32("10.00")); // Will generate an error.
If you change your ToString("00.00") to ToString("00") it will work.
Although in general, I would prefer Int.TryParse so you can handle the error conditions. The following would return -1, if there is a parsing failuer (which there will be).
int cvt;
Console.WriteLine(Int32.TryParse("10.00", out cvt)?cvt:-1);
Yout problem is probably inside your if
if (Conversion.Val(subtotal.ToString()) > Conversion.Val(Dt.Rows[indx]["AdvancePayment"]))
The value of Dt.Rows[indx]["AdvancePayment"] is probably dynamic type, but as int not string. You used a ToString() method to calculate the same kind of value of the total variable. So, the sugestion is use ToString( inside the if too:
if (Conversion.Val(subtotal.ToString()) > Conversion.Val(Dt.Rows[indx]["AdvancePayment"].ToString()))
Please, next time tell us the line that the error throwed, or a better code (it depends your programming expecience)
I'm trying to parse user entered text into a float so that I can perform some wicked awesome math on the result. The result being the numberA variable at the end there. This is how I'm parsing the string into a float:
numberAString = GUI.TextField(new Rect(25, 100, 100, 25), numberAString.ToString());
bool ParsableCheckA = float.TryParse(numberAString, out numberA);
I eventually multiply numberA by another float later. I'm handling text that won't parse with a simple error message later. Couple things that bug me:
1) Why do I need to use numberAString in the TryParse parameters instead of its value? Why can't I just drop GUI.Textfield etc. into that slot? Why do I need to break this up over two lines of code?
2) I get a warning that I never use ParsableCheckA (which is true). But without it, I can't seem to use that Tryparse helper, no? Is there a way to eliminate the need for that bool? Thanks.
TryParse() Metod and its usage is rather straighforward, as shown in the following example:
double _dblOriginal;
_dblOriginal=3.141592;
string _str;
_str = _dblOriginal.ToString();
double _dblParsed;
bool _parseOK= TryParse(_str, out dblParsed);
More details in: http://msdn.microsoft.com/en-us/library/system.double.tryparse%28v=vs.110%29.aspx
Note: make sure that in your example the string numberAString you pass to the TryParse() method contains a valid number.
Also, FYI: TryParse() method has some performance benefits compare to just Parse() method because it does not throw an exception if parsing fail (instead you just check the bool result value).
Hope this will help. Regards,
(1) numberAString (see GUI.TextField) is a string, so you can use it directly in the TryParse() call.
(2) TryParse() is designed to return a boolean value so you can check for errors and take action. However, you aren't required to assign the return value. You can us it like this and simply accept the default value (0.0) assigned to the out parameter:
float.TryParse(numberAString, out numberA);
In this case you would not be able to distinguish between an invalid entry and a value that parsed correctly as zero.
I personally create an extension method to make my number parsing easier. If performance is critical, then this may not be a good idea (because for valid floats, you'll be essentially converting them twice). But I don't the effect on performance is much more than negligible.
public static class NumberExtensions
{
//Test if the text represents a valid float.
public static bool IsFloat(this string text)
{
float dummy = 0;
return Float.TryParse(text, out dummy);
}
//Convert the text to a float. Will throw exception if it's not a valid float.
public static float ToFloat(this string text)
{
float number = Float.Parse(text);
return number;
}
}
Usage...
string text = "123";
if(text.IsFloat())
{
//text must be a valid float
float myfloat = text.ToFloat();
}
else
{
//text isn't a valid float
}
You have to remember to test if it's a float by calling the IsFloat() extension method, but it's much easier for me to think of it conceptually like this rather than using out variables, which some think is a bad idea.
I wrote a piece of simple code that I dont to find what the problem.
the code is:
var sortSecurities="SELECT * FROM securities";
int total=0;
var value="";
foreach(var row in db.Query(sortSecurities))
{
value=row.lastGate;
total=Convert.ToInt32(value)*100;// here the problem with compilation..
db.Execute("INSERT INTO holding(IDgrossPortfolio,IDSecurity,totalHolding,units,buyGate) "+"VALUES (#0,#1,#2,#3,#4)",row.category,row.number,total,"100",row.lastGate);
}
what the problem with the convert?
the error is:
Exception Details: System.FormatException: Input string was not in a correct format.
value does not hold a value that can be converted to Int32. If you could do some debugging and see what the value of it is from row.lastGate, you might see what the problem is.
Also, not sure what is returned by db.Query(sortSecurities) (or really what kind of object row.lastGate is), but you can also try to change value=row.lastGate; to value=row.lastGate.ToString();
you can use try parse to check if the value actually contains a number
int total;
bool result = Int32.TryParse(value, out total);
if (result)
{
db.Execute("INSERT INTO holding(IDgrossPortfolio,IDSecurity,totalHolding,units,buyGate) "+"VALUES (#0,#1,#2,#3,#4)",row.category,row.number,total,"100",row.lastGate);
}
Your value isn't successfully being parsed by Convert.ToInt32()
Alternatively, consider using Int32.TryParse() and validate if the data is indeed the type of data you're expecting.
int result;
if(Int32.TryParse(row.lastGate, out result))
{
//row.lastGate was a valid int
total = result * 100;
}
else
{
//row.lastGate wasn't a valid int
}
Thanks you for all... I try now and found elegant answer.
Like I wrote in the comments, becouse I know that the value of row.lastGate
represent a number I don't need to check it.
So I try this and it works:
var sortSecurities="SELECT * FROM securities";
int total=0;
double value=0;
foreach(var row in db.Query(sortSecurities))
{
value=Convert.ToDouble(row.lastGate);
total=Convert.ToInt32(value)*100;//100 is default
db.Execute("INSERT INTO holding(IDgrossPortfolio,IDSecurity,totalHolding,units,buyGate) "+"VALUES (#0,#1,#2,#3,#4)",row.category,row.number,total,"100",row.lastGate);
}
Probably I needed to change the value first of all to double and then to int
Becouse when I try to change it directly to int the Compiler did'nt interpret the
string right, becouse of the dot in the number (type double).
thanks about the the intention..
Working on parsing from a text box to int to get into the incrementHour method as shown.
if (txtHourPlus.Text != String.Empty)
{
time1.incrementHour(int.Parse(txtHour.Text));
}
And in the time class: (the time1 objects class)
public int incrementHour(int step)
{
if (step > 0 && hour < 24)
{
//step = step % hour;
hour = (hour + step) % 24;
time.AddHours(hour);
return hour;
}//end of if
else
{
MessageBox.Show("Please enter a positive number.");
return 0;
}//end of else
}//end of incrementHour
not sure why i'm getting this error. I'm converting it to the corrent data type. Because it accepts an int variable.
Alright well i got it to take the value (small mistake >.> Don't even wanna say it)
However as someone already said the method probably needs work because i'm trying to change the Datetime value that i get in the first place and add an hour or subtract and etc etc.
That will happen if someone has typed "foo" into the text box, for example. You should use int.TryParse instead, which lets you detect the error without an exception being thrown.
I notice that you're not actually using the return value of your method though - just like you're not using the return value of time.AddHours. You are aware that DateTime.AddHours doesn't actually modify the value you're calling it on, aren't you? (I suspect you'll need to tweak that method quite a bit, actually... there are various potential problems with it, depending on exact what you're trying to do.)
(Finally, I'd change the method name to IncrementHour to comply with .NET conventions.)
you are testing txtHourPlus for emptiness, but then parsing and passing txtHour. typo (?)
If your input isn't parsable as an integer, attempting to parse it will raise an exception. Validate or use Int32.TryParse()
Change this part of your code:
if (txtHour.Text != String.Empty)
{
int parsedValue;
if (int.TryParse(txtHour.Text, out parsedValue))
{
time1.incrementHour(parsedValue);
}
else
{
// non-numeric value was entered into the textbox - handle accordingly.
}
}