What's this =! operator? [duplicate]

Answer 1

I think this is one of the writing or printing mistake. Because if we can not compile this code as it holds a compiletime error. And here this is inside if clause, the return type must be boolean. So how can it possible. The answer is simply a mistake or as Mike said obfuscated way of writing.

And only possible if both variables a and b are boolean which will be compiled as a is equal to (not)b i.e (a = !b) .

Answer 2

That's two operators, = and !, not one. It might be an obfuscated way of writing

a = !b;
if (a) {
    // whatever
}

setting a to the logical inverse of b, and testing whether the result is true (or, equivalently, whether b was false).

Or it might be a mistyping of a != b.

Answer 3

a =! b 

is just a funny way of putting

a = !b

i.e. the assignment of not b to a.

The value of the expression is a after the assignment.

With the code below you can see that the value of the expression a = !b is !false (i.e. true), and you can then see the assignment has taken place by checking the value of a, which is also true.

#include <iostream>

int main() 
{ 
    bool a = false;
    bool b = false;

    if(a)
        printf("a is true!\n");
    else
        printf("a is false!\n");

    if(a = !b)
        printf("expression is true!\n");
    else
        printf("expression is false!\n");

    if(a)
        printf("a is true!\n");
    else
        printf("a is false!\n");

}

Result:

a is false!
expression is true!
a is true!

Answer 4

They are two different operators: the = (assignment) operator together with the ! operator. It can basically be translated to an assignment of a to the negated value of b.

if (a = !b)

But, what the user, probably, meant to write was the != operator:

if (a != b)

Answer 5

There could be three reasons for this:

1. It could be a mistyping of the != operator, meaning not equal to. Example:

   if (a != b) {
       // a is not equal to b
   }
   

2. It could be a mistyping a == !b, meaning a is equal to not b, which would most commonly be used with booleans. Example:

   if (a == !b) {
       // The boolean a is equal to not b (a is not equal to b)
   }
   

3. It could be trying to assign a to the inverse of b. Example:

   bool a = !b; // Sets a to the opposite of b
   

Answer 6

This is all about clarity of code:

It should be written as: if (a = !b)

if (a = !b) is the same as saying if a is assigned to !b. So there are technically 2 separate operators being used, = which is an assignment operation, and ! which is a logical expression.

Just put a space between = and ! it solves this confusion.