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Checking if user input is a letter [duplicate]

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Identify if a string is a number
(26 answers)
Closed 5 years ago.
I'm receiving some user input through a TextBox which is then being converted to an int so it can be used in further calculations when I click the Calculate button.
I have checked to see if the TextBox is empty when the Calculate button is clicked, if it is, then a message box appears. Now I realised I need to check to make sure it is a number being input, not a letter. I'm looking for something similar to this
if(hoursInput.Text == "" || hoursInput.Text contains "a-z")
{
\\ handle error
}
else
{
\\ continue with code
}
EDIT:
The user input is converted to an int in the else block, but I do not want the function to reach this stage of converting from string to int if the user input contains letters, which is why I want to check to see if the user input contains any letters in the if block

As mentioned, use Int32.TryParse which will return a bool of whether or not the input could be parsed to an Int32. One of the parameters is an out and will become the Int32 if the input could be parsed.
See:
https://msdn.microsoft.com/en-us/library/f02979c7(v=vs.110).aspx
if(hoursInput.Text == "" || !Int32.TryParse(hoursInput.Text, out number))
{
\\ handle error
}
else
{
\\ continue with code
}

You really don't need to check anything explicitly:
int aNumber;
if (!Int32.TryParse(hoursInput.Text, out aNumber)) {
// handle error
} else {
// handle `aNumber`
}

Replace string value with '0' when string is empty

I'm taking a value from a textbox and converting it to decimal. But, the textbox value could be empty. So, how could I handle empty strings from the textbox?
Unfortunately I have around 50 textboxes to deal with, so answers like 'check for null with IF condition' won't help me. My code will look ugly if I use all those IF conditions.
I have this
Convert.ToDecimal(txtSample.Text)
To handle nulls, I did this
Convert.ToDecimal(txtSample.Text = string.IsNullOrEmpty(txtSample.Text) ? "0" : txtSample.Text)
But, the above code is displaying '0' in the textbox. User does not want to see '0'. Another solution is to take text box value into a variable and convert the variable like below.
string variable = txtSample.Text;
Convert.ToDecimal(variable = string.IsNullOrEmpty(variable) ? "0" : variable)
But again, I do not want to define around 50 variables. I am looking for some piece of code that handles null values during conversion without adding the extra line of code.

But, the above code is displaying '0' in the textbox. User does not want to see '0'.
This is because your statement is assigning the new value to txtSample.Text (when you do txtSample.Text = ...). Just remove the assignment:
Convert.ToDecimal(string.IsNullOrEmpty(txtSample.Text) ? "0" : txtSample.Text)
To make things easier if you have many text fields to handle, you can define an extension method :
public static string ZeroIfEmpty(this string s)
{
return string.IsNullOrEmpty(s) ? "0" : s;
}
And use it like this:
Convert.ToDecimal(txtSample.Text.ZeroIfEmpty())

You could make a function to keep from copying the code all over the place.
decimal GetTextboxValue(string textboxText)
{
return Convert.ToDecimal(string.IsNullOrEmpty(textboxText) ? "0" : textboxText);
}
and then use it like this:
GetTextboxValue(txtSample.Text);

You can create an extension method for the string as below
public static decimal ToDecimal(this string strValue)
{
decimal d;
if (decimal.TryParse(strValue, out d))
return d;
return 0;
}
Then you can just txtSample.Text.ToDecimal() in every place.

Check if a NumericUpDown has no value

How can I check if a user has left a NumericUpDown control empty? I have seen on another question to check the 'Text' property but there is no text property to check against.

You can check against the Text property, although it is hidden from the designer and IntelliSense.
Just try this sample. It does work:
if (string.IsNullOrEmpty(control.Text))
{
// no value
}

You can use ,
if(NumericUpDown.Text == "")
{
// If the value in the numeric updown is an empty string, replace with 0.
NumericUpDown.Text = "0";
}

On inserting to a database with predefined value C#

OK I have a text box with a set value, I only want this set value sent if the text box is not filled in on completion of form.
code
dontaion_euro.Text = "99.00";
problem is when I click send it only sends the data 99.00 I only want this sent if blank.
how could I achieve this?

Step1 : you need to Trim the Textbox value to remove the white spaces.
Step2 : you can compare the Textbox value with Empty String to check whether Textbox value is Empty or not
Try this:
if(donation_euro.Text.Trim().Equals(""))
{
donation_euro.Text="99.00";
}

If I understand correctly, you can use String.IsNullOrEmpty method like;
Indicates whether the specified string is null or an Empty string.
if(string.IsNullOrEmpty(dontaion_euro.Text))
{
dontaion_euro.Text = "99.00";
}
else
{
//Your textbox is not null or empty
}

Trim Method Doesn't Clear All Spaces

Hi i'm working on a basic windows form in c# and I have a little problem with the Trim() method.
There are 3 text boxes in witch the user enters his first name, last name and an ID.
Then he can save the info by clicking on a save button but I want to make sure that he doesn't leave blank boxes so I do the following test:
string CFN = Curator_FN.Text;
string CLN = CURATOR_LN.Text;
string CID = CURATOR_ID.Text;
Curator_FN.Text.Trim();
CURATOR_ID.Text.Trim();
CURATOR_LN.Text.Trim();
if (((Curator_FN.Text.Length == 0) || (CURATOR_ID.Text.Length == 0) || (CURATOR_LN.Text.Length == 0)))
{
MessageBox.Show("You Have to enter a First Name, a Last Name and an ID");
Empty = true;
}
The problem is if I just make some blank space with the space bar the Trim() method doesn't consider them as a blank space..
Maybe I just misunderstand the Trim() method and if I do, do you have any idea on how I could do the this?
Thanks in advance.

The Trim method does not modify the contents of the text boxes, it simply returns the trimmed version. You need to store this version, for example
Curator_FN.Text = Curator_FN.Text.Trim();
Of course this has the potential to make changes visible to the user (and it also has to access the UI thread which under other circumstances might be a problem), so it is far better to use a local variable as in
var curatorFn = Curator_FN.Text.Trim();
// etc
if (curatorFn.Length == 0 || ... ) {
// show messagebox
}
Of course if this is all you need to do, using string.IsNullOrWhiteSpace might be a more convenient alternative.

Since strings are immutable in C#, the Trim() method doesn't change the string itself; it returns a new instance of the trimmed string.
You need to assign the results of the method calls to the variables, i.e.
CFN = Curator_FN.Text.Trim()
And then check whether or not CFN is empty.

Trim does not modify the string. You want:
Curator_FN.Text = Curator_FN.Text.Trim();
CURATOR_ID.Text = CURATOR_ID.Text.Trim();
CURATOR_LN.Text = CURATOR_LN.Text.Trim();
Also, if you're using .NET 4 you might want to check into the String.IsNullOrWhiteSpace method as well.
if (String.IsNullOrWhiteSpace(Curator_FN.Text) ||
String.IsNullOrWhiteSpace(CURATOR_ID.Text) ||
String.IsNullOrWhiteSpace(CURATOR_LN.Text)
{
//..
}

Trim does not modify the string itself. It returns a new trimmed string.
If you don't really care about modifying the variable, look at the IsNullOrWhiteSpace method.
if (String.IsNullOrWhiteSpace(curatorFn) || ... ) {
// show messagebox
}