What Does the Tilde Mean in an Expression

What does the tilde mean in an expression?

That is the bitwise complement operator, also known as bitwise negation.

What does a tilde do when it precedes an expression?

~ is a bitwise operator that flips all bits in its operand.

For example, if your number was 1, its binary representation of the IEEE 754 float (how JavaScript treats numbers) would be...

0011 1111 1111 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000

So ~ converts its operand to a 32 bit integer (bitwise operators in JavaScript do that)...

0000 0000 0000 0000 0000 0000 0000 0001

^{If it were a negative number, it'd be stored in 2's complement: invert all bits and add 1.}

...and then flips all its bits...

1111 1111 1111 1111 1111 1111 1111 1110

So what is the use of it, then? When might one ever use it?

It has a quite a few uses. If you're writing low level stuff, it's handy. If you profiled your application and found a bottleneck, it could be made more performant by using bitwise tricks (as one possible tool in a much bigger bag).

It's also a (generally) unclear trick to turn indexOf()'s found return value into truthy (while making not found as falsy) and people often use it for its side effect of truncating numbers to 32 bits (and dropping its decimal place by doubling it, effectively the same as Math.floor() for positive numbers).

I say unclear because it's not immediately obvious what it is being used for. Generally, you want your code to communicate clearly to other people reading it. While using ~ may look cool, it's generally too clever for its own good. :)

It's also less relevant now that JavaScript has Array.prototype.includes() and String.prototype.includes(). These return a boolean value. If your target platform(s) support it, you should prefer this for testing for the existence of a value in a string or array.

What is meaning of tilde(~) symbol mean in the context of this PHP documentation page?

Edit: I've submitted a patch to fix it to the PHP documentation and it got accepted, the new phrasing is "approximately 1.9e308".

It means "approximately" in this context, even though the sentence is poorly phrased, due to the very ambiguousness you cite.

There's no mathematical or programmatic meaning behind the symbol in this particular context, although as you said, in a program, ~ means the bitwise not operator.

My guess is that it was written without thought of the other meanings of ~ preceding a number.

What is the purpose of this tilde in C#

From the ~ Operator documentation:

The ~ operator performs a bitwise complement operation on its operand, which has the effect of reversing each bit. Bitwise complement operators are predefined for int, uint, long, and ulong.

For example:

unsigned int i = ~0;

Result: Max number I can assign to i

and

signed int y = ~0;

Result: -1

so fore more info we can say that ~0 is just an int with all bits set to 1. When interpreted as unsigned this will be equivalent to UINT_MAX. When interpreted as signed this will be -1

What is meaning of first tilde in purrr::map

As per the map help documentation, map needs a function but it also accepts a formula, character vector, numeric vector, or list, the latter of which are converted to functions.

The ~ operator in R creates formula. So ~ lm(mpg ~ wt, data = .) is a formula. Formulas are useful in R because they prevent immediate evaluation of symbols. For example you can define

x <- ~f(a+b)

without f, a or b being defined anywhere. In this case ~ lm(mpg ~ wt, data = .) is basically a shortcut for function(x) {lm(mpg ~ wt, data = x)} because map can change the value of . in the formula as needed.

Without the tilde, lm(mpg ~ wt, data = .) is just an expression or call in R that's evaluated immediately. The . wouldn't be defined at the time that's called and map can't convert that into a function.

You can turn these formulas into functions outside of the map() with purrr::as_mapper() function. For example

myfun <- as_mapper(~lm(mpg ~ wt, data = .))
myfun(mtcars)
# Call:
# lm(formula = mpg ~ wt, data = .)
# 
# Coefficients:
# (Intercept)           wt  
#      37.285       -5.344  

myfun
# <lambda>
# function (..., .x = ..1, .y = ..2, . = ..1) 
# lm(mpg ~ wt, data = .)
# attr(,"class")
# [1] "rlang_lambda_function"

You can see how the . becomes the first parameter that's passed to that function.

What do the dot (.) and the tilde (~) represent in R?

This is the "Formula" syntax
~ is read as "in function of"
and . means all other variables
in this case you have
load_result in function of every other variable except annual_income

What does this symbol ~ do in matlab

The tilde in that expression is used to ignore the first return value from the min function. That syntax has only been around for a few years, it's possible the error is occurring because you're using an older version of MATLAB.

Try replacing the ~ with idx. That'll cause the second return value to overwrite the first one, and will be functionally equivalent to the code you've posted.

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In other contexts, ~ is the logical not operator and ~= is a logical comparison operator for testing inequality.

What does tilde(~) operator do?

The ~ operator in C++ (and other C-like languages like C and Java) performs a bitwise NOT operation - all the 1 bits in the operand are set to 0 and all the 0 bits in the operand are set to 1. In other words, it creates the complement of the original number.

For example:

10101000 11101001 // Original  (Binary for -22,295 in 16-bit two's complement)
01010111 00010110 // ~Original (Binary for  22,294 in 16-bit two's complement)

In your example, ch=~((ch^i)) performs a bitwise NOT on the bitwise XOR of ch and i then assigns the result to ch.

The bitwise NOT operator has an interesting property that when applied on numbers represented by two's complement, it changes the number's sign and then subtracts one (as you can see in the above example).

You may want become familiar with the different operators of the C++ language since it is difficult to search for operators on search engines. Better yet, you can get a good C++ book which will tell you about the C++ operators.

In the C language, what does return ~0 mean?

~ is a bitwise not/complement, aka it changes all 0's to 1's and vice-versa. ~0 is a value with all bits set to 1.

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