I was writing a very simple PHP code on notepad (I don't know if that will even work), but when I uploaded onto the file manager, it came out as untitled.php.txt. Now that means it's just a text file with a strange title. I didn't notice this at first and continued putting other PHP code on existing pages and it didn't work. I'm assuming that since the file was untitled.php.txt (even though I renamed it without the .txt) and the PHP code didn't work on the existing page, it means that changing the extension won't change the file. So what program do I use to write PHP code? (I use Notepad for everything, .html, .css, and .js)
Notepad saves everything as .txt unless, when you save it, you change "Save as type" to "All files." If you don't do that, Notpad will just add ".txt" to whatever you put in. Thus, if you put "abc.php" in the box, you did NOT rename without the ".txt" since Notepad will just add it on. If you were to do the same thing with "Save as type" set to "All files," the file really will be saved as "abc.php" without the ".txt" extension.
Right now, if you rename the files on your system using Explorer (for your local editing) and rename the files in your hosting account using the File Manager, they should work, as long as your actual coding is correct.