I am confused and couldn't figure out the difference between these two lines!!

```
echo "<li><a href='category-".$row['id'].".php' >".$row['name']."</a></li>";

```

The first one echos categories I displayed in a home page. It works fine and I don't have to create the category.php file.

```
echo "<li><a href='category-.php".$row['id']."' >".$row['name']."</a></li>";

```

But the second code it tells me file doesn't exist. 

So my question is, why the first code doesn't require the file but the second code does?