Why Does Single '=' Work in 'If' Statement

Why does single `=` work in `if` statement?

The only necessary thing for an if statement to be valid is a boolean expression. In this case, since = returns the result of the assignment, what's actually being tested is the falsiness of session["devise.facebook_data"].

IntelliJ has a good point to lodge a complaint about code like this, as it's difficult to read without knowing a thing or two about Ruby. A recommendation would be to move that to an explicit assignment statement instead. This has the added benefit of DRYing up a reference to it twice.

class User < ActiveRecord::Base
  def self.new_with_session(params, session)
    super.tap do |user|
      data = session["devise.facebook_data"]
      if data && data["extra"]["raw_info"]
        user.email = data["email"] if user.email.blank?
      end
    end
  end
end

How does the single equal sign work in the if statement in javascript

The first part of your analysis is of course correct.

Now, the interesting part might be why your last code if (var ...) { doesn't work.

It doesn't work because

1)

var something

is a statement, not an expression.

2) here's how ECMAScript defines the if statement :

IfStatement :

if ( Expression ) Statement else Statement

if ( Expression ) Statement

You must put an expression in the if clause, not a statement.

More on expressions vs statement in this article.

A php if statement with one equal sign...? What does this mean?

It's a form of shorthand, which is exactly equivalent to this:

$confirmation = $payment_modules->confirmation();
if ($confirmation) {

}

If statement always giving the same answer

You are assigning the value true to enoughtreats.

Try using the equality operator rather than assignment:

if (enoughtreats == true) {
...
}

or simply:

if(enoughtreats) {
...
}

What does = instead of == mean in c if statement?

= is an assignment operator in C. According to C99 6.5.16:

An assignment operator stores a value in the object designated by the
left operand. An assignment expression has the value of the left
operand after the assignment, but is not an lvalue.

It means that expression a = 5 will return 5 and therefore instructions inside if block will be executed. In contrary, if you replaced it with a = 0 then 0 would be returned by assignment expression and instructions inside if would not be executed.

Use and meaning of in in an if statement?

It depends on what next is.

If it's a string (as in your example), then in checks for substrings.

>>> "in" in "indigo"
True
>>> "in" in "violet"
False
>>> "0" in "10"
True
>>> "1" in "10"
True

If it's a different kind of iterable (list, tuple, set, dictionary...), then in checks for membership.

>>> "in" in ["in", "out"]
True
>>> "in" in ["indigo", "violet"]
False

In a dictionary, membership is seen as "being one of the keys":

>>> "in" in {"in": "out"}
True
>>> "in" in {"out": "in"}
False

can you have two conditions in an if statement

You can use logical operators to combine your boolean expressions.

• && is a logical and (both conditions need to be true)
• || is a logical or (at least one condition needs to be true)
• ^ is a xor (exactly one condition needs to be true)
• (== compares objects by identity)

For example:

if (firstCondition && (secondCondition || thirdCondition)) {
    ...
}

There are also bitwise operators:

• & is a bitwise and
• | is a bitwise or
• ^ is a xor

They are mainly used when operating with bits and bytes. However there is another difference, let's take again a look at this expression:

firstCondition && (secondCondition || thirdCondition)

If you use the logical operators and firstCondition evaluates to false then Java will not compute the second or third condition as the result of the whole logical expression is already known to be false. However if you use the bitwise operators then Java will not stop and continue computing everything:

firstCondition & (secondCondition | thirdCondition)

JavaScript - returning true even though condition is not fulfilled

The condition is always true, because you assign this value to the variable and this is the value which is evaluated for the if clause.

But you could use a direct check without a compare value (and without assigning this value).

Beside that, you could change the else part to only an if part, becaue you exit the function with return, so no more else happen in this case.

if (usernameExists) {
    console.log("returning true");
    return true;
}
if (looped) {
    console.log(usernameExists+" is returned");
    looped = null;
    return false;
}

Are double square brackets [[ ]] preferable over single square brackets [ ] in Bash?

[[ has fewer surprises and is generally safer to use. But it is not portable - POSIX doesn't specify what it does and only some shells support it (beside bash, I heard ksh supports it too). For example, you can do

[[ -e $b ]]

to test whether a file exists. But with [, you have to quote $b, because it splits the argument and expands things like "a*" (where [[ takes it literally). That has also to do with how [ can be an external program and receives its argument just normally like every other program (although it can also be a builtin, but then it still has not this special handling).

[[ also has some other nice features, like regular expression matching with =~ along with operators like they are known in C-like languages. Here is a good page about it: What is the difference between test, [ and [[ ? and Bash Tests

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