How enter variable or function in php code

Question

How enter variable or function in php code, for example, <?php
$myfile = fopen("names.txt", "x+");

$txt = "Y\n";
Y=+=Y;;
if Y>0
echo Y
fwrite($myfile, $txt);

fclose($myfile);

$read = file('names.txt');
foreach ($read as $line) {
echo $line .", ";
}
?>

Answer 1

check through the question and edit
I don't understand what you are trying to ask

// also there are some errors in your code