Got Error: Return an Empty String to Bool

Got error : return an empty string to bool

Make the empty check first

func beginsWithVowel(x: String) -> Bool {
    if x.isEmpty { return false }
    if x.characters[x.startIndex] == "a" { ...

Slightly different approach using regular expression, it includes the empty check:

func beginsWithVowel(x: String) -> Bool {
    let regex = try! NSRegularExpression(pattern: "^[aeiou]", options: .caseInsensitive)
    return regex.firstMatch(in: x, range: NSMakeRange(0, x.utf16.count)) != nil
}

In javascript, is an empty string always false as a boolean?

Yes. Javascript is a dialect of ECMAScript, and ECMAScript language specification clearly defines this behavior:

ToBoolean

The result is false if the argument is the empty String (its length is zero);
otherwise the result is true

Quote taken from http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf

Converting from a string to boolean in Python

Really, you just compare the string to whatever you expect to accept as representing true, so you can do this:

s == 'True'

Or to checks against a whole bunch of values:

s.lower() in ['true', '1', 't', 'y', 'yes', 'yeah', 'yup', 'certainly', 'uh-huh']

Be cautious when using the following:

>>> bool("foo")
True
>>> bool("")
False

Empty strings evaluate to False, but everything else evaluates to True. So this should not be used for any kind of parsing purposes.

c# default value for Convert.ToBoolean

This is slightly diffrent logic, but this will give you false for any value that does not correctly convert in to a Boolean which is likely what you are really looking for.

string temp = "";
bool result
if(!bool.TryParse(temp, out result))
{
    result = false; //This line and the `if` is not actually necessary, 
                    //result will be false if the parse fails.
}

SilentUpdate = result;

How do I check for an empty/undefined/null string in JavaScript?

Empty string, undefined, null, ...

To check for a truthy value:

if (strValue) {
    // strValue was non-empty string, true, 42, Infinity, [], ...
}

To check for a falsy value:

if (!strValue) {
    // strValue was empty string, false, 0, null, undefined, ...
}

---

Empty string (only!)

To check for exactly an empty string, compare for strict equality against "" using the === operator:

if (strValue === "") {
    // strValue was empty string
}

To check for not an empty string strictly, use the !== operator:

if (strValue !== "") {
    // strValue was not an empty string
}

Convert string to boolean in C#

I know this is not an ideal question to answer but as the OP seems to be a beginner, I'd love to share some basic knowledge with him... Hope everybody understands

OP, you can convert a string to type Boolean by using any of the methods stated below:

 string sample = "True";
 bool myBool = bool.Parse(sample);

 // Or

 bool myBool = Convert.ToBoolean(sample);

bool.Parse expects one parameter which in this case is sample, .ToBoolean also expects one parameter.

You can use TryParse which is the same as Parse but it doesn't throw any exception :)

string sample = "false";
Boolean myBool;

if (Boolean.TryParse(sample , out myBool))
{
    // Do Something
}

Please note that you cannot convert any type of string to type Boolean because the value of a Boolean can only be True or False

Hope you understand :)

How do I convert/cast a string into a bool in Tcl?

After thinking some more, and looking some more, the answer probably should be: "It depends"

With my perl background I was expecting something similar to perl. My fault.

In Tcl string is true seems to be the official cast function. Valid strings for casting are defined here:

If string is any of 0, false, no, or off, then Tcl_GetBoolean stores a
zero value at *boolPtr. If string is any of 1, true, yes, or on, then
1 is stored at *boolPtr. Any of these values may be abbreviated, and
upper-case spellings are also acceptable

In my case, I don't care about the string's content so I can just

if {[string length [some_func $some_args]] > 0} {
  ...
}

Another way to write this also is much simpler:

if {[some_func $some_args] != {}} {
  ...
}

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