Functions within functions

Why is it bad practice?

a.php

<?php

function a1()
{
   b();
   c();
}

function b()
{
}

function c()
{
}

?>

I hope you want some information regarding class and object.

Maybe you need a recursive function?

function do_something_to($input) {
   // Do something to $input
   
   // Check the value of $input after doing something
   if ($input != "something") {
      do_something_to($input);
   }
   return $input;
}

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This function will continue to call itself recursively until $input = something. If you provided more detail on what you want to achieve, I may be able to provide a more specific answer.

Actually, your question is too general.  Without test data for input and a goal for the output, it is impossible to give a good answer.  

When you consider that virtually all programming methods and structures were invented before 1970, I always search to see if my problem has been answered already.  And it usually has by people smarter than me.  I just have to provide the specific data and conditions for my application.

+1 for what @DaveBaldwin wrote.

This question makes it sound like you are new to programming or at least you do not have a depth of experience in computer science.  To that end, we have an article here at EE that will help you get the foundation you need.  Don't expect it to come all at once -- it takes time and structured learning to develop any activity to the point of proficiency!
https://www.experts-exchange.com/Web_Development/Web_Languages-Standards/PHP/A_11769-And-by-the-way-I-am-new-to-PHP.html

Now to the specifics of your question, as much as can be discerned... Don't ever design an application like this!  The more nesting and complexity you bring to application design, the more likely your application will fail (Obamacare website).  Instead reduce the elements of application design to the SSCCE.  Then build the application back up using that collection of small, correct examples.  When you learn object-oriented design (perhaps the only meaningful advance in programming methods since 1970) you will find that the encapsulation of functionality makes a great deal of sense, and doesn't create anything as complicated as functions within functions.

@kaufmed
Because it may never leave the loop - and you end up with a infinite loop.

@GaryC123

You can code just about any loop into an infinite one! Does that mean all loops are bad practice  ; )

The short of it is I don't see anything wrong with the loop. As with anything in programming, care should be taken--in this case to avoid infinite loops (unless that is what you actually need!).

I'm creating a form validation but it runs into errors if I submit it past the normal amount of time regarding class (color) of what needs to be fixed, not the printing of the variables themselves.

Debugging wise I guessed it must be that the script doesn't run the section that determines variables aren't empty.

So I was thinking programming wise have a main function that has other functions to ensure it does everything it needs to every time.

An infinite loop would be desirable, or a counter that would stop eventually. That's really not necessary though.

edit: determines whether or not variables are empty and assigns the css class

I just debugged more and that is exactly what is happening because it won't accept valid submissions.

After the second submit it stops working. I'm going to check these codes and whichever one works gets points.

This will work for what I'm doing. I just thought pass/returning a variable would be better but it's not much different function wise I guess.

If you want to post a more specific question, perhaps including a code example and some test data, we may be able to share some good design patterns.  Just a thought. ~Ray

If all loops are bad, and bad is evil, are all loops evil?
Not saying all loops are bad, but without some get out of jail clause they are.