print out the content of a modified file

I am having a problem with outputting a modified file in php, here is my code:

<?php
$content = file_get_contents("1.txt");
$items = explode("\n",$content);
$line = ""; 
foreach ($items as $item){
$values = explode(",",$item);
foreach ($values as &$value){
    $key = array_search($value,$values);
    if ($key!=4){
        $line .= $val开发者_如何学Cue.",";
    }
    elseif ($value=="0"){
        $value="?";
        $line .= $value."\n";
    }
    else $line .= $value."\n";
}
}
$file = fopen("1.txt","w");
fwrite($file,$line);
fclose($file); 
?>

The original content in 1.txt is

1,1,1,1,1
2,2,2,2,0

The desired output is to be

1,1,1,1,1
2,2,2,2,?

However, I got this when I run the script:

1,1,1,1,1,2,2,2,2,?
,

What is the problem of my script? Thanks a lot!

You are not connecting lines with \n correctly. Here's my bit modified function:

$content = '1,1,1,1,1
2,2,2,2,0';

$lines = explode("\n", $content);

$modLines = array();

foreach ($lines as $line)
{
    $values = explode(',', $line);

    foreach($values as &$value)
    {
        # Do here what ever you want to
         if($value == '0')
        $value = '?';
    }

    $modLines[] = implode(',', $values);

}

$content = implode("\n", $modLines);

echo $content;

Returns

1,1,1,1,1
2,2,2,2,?