如何使用变量作为运算符？

Question

how can I do this?

$v1=105;
$v2=90;
if ($value=='subtraction'){
    $operator='-';
}else{
    $operator='+';
}

$new_value=$v1.$operator.$v2;

So it should return 105-90=15 or 105+90=195. But how can I use the $operator variable as a operator? For example this doesn't work:

eval("$new_value=$v1".$operator."$v2");

Thanks for the help!

Answer 1

I suggest not doing this, but to use eval, you'd have to do it like this:

// You need to escape the $ in $new_value
eval("\$new_value = $v1 $operator $v2");

I suggest doing it something like this instead (ie: Don't use a variable for operator, just do the calculation):

$v1=105;
$v2=90;
if ($value=='subtraction'){
    $new_value= $v1 - $v2;
}else{
    $new_value= $v1 + $v2;
}