PHP logic if statments

Question

I have this code:

$distance= -1 ;//default
//distance calc
if($dgalaxy = $galaxy){
    if(($dx = $x) && ($dy = $y))
    {
            //inter planitary currently unknown formula
    }else{
            $distance = round(Sqrt(pow(($dx-$x),2)+pow(($dy-$y),2)));//interstllar
    }
}else{//intergalatic
    if ($galaxy < $dgalaxy){
            $distance = (((9-fmod($galaxy,10))*200)+2000+(fmod($dgalaxy,10)*200));//anti clockwise galactic
    }else{
            $distance = (((fmod($galaxy,10))*200)+2000+(fmod(9-$dgalaxy,10)*200));//clockwise galactic
    }
}

It should return a value for each calculation except for the inter planetary clause. for interstellar (when ($dgalaxy = $galaxy) and the x,y coordinates differ) this runs the interstellar formula and this works fine.

But, when $dgalaxy != $galaxy, it returns with -1 which means that it is not running either of the galactic distance calculations!

What have I done wrong and how can I fix it?

Answer 1

$dgalaxy = $galaxy is an assignment not a comparison. Use ==.

Ditto elsewhere.

Answer 2

You use = instead of == or ===:

$distance= -1 ;//default
                //distance calc
                // MISTAKE HERE. USE == INSTEAD of =
                if($dgalaxy == $galaxy){
                        if(($dx == $x) && ($dy == $y))
                        {
                                //inter planitary currently unknown formula
                        }else{
                                $distance = round(Sqrt(pow(($dx-$x),2)+pow(($dy-$y),2)));//interstllar
                        }
                }else{//intergalatic
                        if ($galaxy < $dgalaxy){
                                $distance = (((9-fmod($galaxy,10))*200)+2000+(fmod($dgalaxy,10)*200));//anti clockwise galactic
                        }else{
                                $distance = (((fmod($galaxy,10))*200)+2000+(fmod(9-$dgalaxy,10)*200));//clockwise galactic
                        }
                }

Answer 3

Shouldn't it be $dgalaxy == $galaxy? I.e. equality check, rather than assignment?