Is there any way to set a non-constant value to a checkbox value?

I have this dynamic checkbox that is passed as an array to my treatment page    link

if($op1== null){
    $op1= "Não";
}
if($op2 == null){
    $op2 = "Não";
}
if($op2 == null){
   $op 2= "Não";
}    
if($op2 == null){
  $op2  = "Não";
}

I tried to put these conditionals on the page, but they only apply to the first array I get and write to the bank, giving me something like this

So,howcanthesevaluesinthecheckboxes,ifnotselected,containthevalue"No", instead of "Yes", when selected?