Constant error 'const' (T_CONST)

PHP does not include $ constants.

const ABBB=300;

However, the error message seems to be saying something different.
Perhaps the problem is something wrong with the previous code, not that line.
Perhaps there is no semicolon ; at the end of the sentence.
Check it out.

PHP does not write constant declarations with const at all variable declaration locations.

(Also, as @ItagakiFumihiko's answer says, we do not add $ to the constant name.)

For example, you can declare class constants as follows:

class MyClass {
    private const INITIAL_COST = 300;
    
    public function getYourAnswer($stack)
    {
        $calcCost=0;
        
        $calcCost=calculate();
        
        $totalCost=$calcCost+MyClass::INITIAL_COST;
        return$totalCost;
    }
}

Is getYourAnswer the class method since it comes with public?
In any case, you cannot define a constant in const within a class method or a normal function.
If you want to define it, it's outside.

class hogehoge{

    const INITIAL_COST = 300;

    public function getYourAnswer($stack)
    {
        $calcCost=0;

        $calcCost=calculate();

        $totalCost=$calcCost+INITIAL_COST;
        return$totalCost;
    }
}

If you want INITIAL_COST to be in the function scope, consider whether it must be a constant.Isn't it okay to use a normal variable?

Also, it has nothing to do with the question, but the code provided contains a full-width space, which also causes an error.

Compared to the declaration in define(), the const keyword has the following limitations:

PHP:Constants Syntax

Note:
 As selected to define constants using define(), constants defined using the const keyword must be degraded at the top-level scope because they are defined at compile-time. This means that they cannot be defined inside functions, loops, or duration.