[SOLVED] Difference between echo and return?

[Gleasonator]

Hi.

 

I'm new to PHP (I'm just learning about functions today), and I have a question regarding "echo" and "return". I do understand that "return" is intended to be used within a function and it seems that it's only intended for use within a function. However, the following is what's puzzling me.

 

This code is from W3C Schools:

 

<?php
function add($x,$y)
  {
  $total = $x + $y;
  return $total;
  }

echo "1 + 16 = " . add(1,16);
?>

 

And it outputs as "1 + 16 = 17" as it should, and I understand why it works.

 

But why can't I use "echo $total;" in the function instead of "return $total;"?

 

Like this:

 

<?php
function add($x,$y)
  {
  $total = $x + $y;
  echo $total;
  }

echo "1 + 16 = " . add(1,16);
?>

 

I've tried this, but the output from this is "171 + 16 ="

 

Yes, using return does work. I'm not asking for a coding solution, I'm merely asking for the logic behind this that makes it function the way it does.

 

I would appreciate it if anyone could take the time to give me some tips. PHP is something I've always wanted to learn, but I want to LEARN it, not just memorize it... so that's why I'm asking this.

[timmah1]

doing what you did, your pretty much echoing the result twice, it's the same as writing

function add($x,$y)
  {
  $total = $x + $y;
  echo $total;
  }

echo "$total" . add(1,16);

 

[teynon]

echo is an output feature. Sort of like a writeln if you use any other languages. return is simple a return of the value. It is only output because you are calling the return command from an echo statement.

 

Hence $value=add(1,16); would do nothing except return the value. Unless the function had an echo in it.

 

You see 171 because the function script is finished and echos before the main echo command is finished.

[chronister]

echo prints something on screen and return gives a value...

 

 

<?php
function addEm()
{
      $result = 1+2;

   return $result
}

$theVar = addEm();

if($theVar => 3)
{
   echo 'It is at least 3';
}
?>

 

Yes in a lot of instances you may want to echo what is returned, but in a lot of instances, you will want to use that value in a comparative or operational sense.

 

Say you have a credit card mod10 check function. (mod10 is an algorithim for determining if a CC num is valid)

 

You will generally not want to echo the result, but compare it to a true/false or 1/0 type value.

 

So in short, echo will print on screen, return gives a value that you can set in a var and use it for echo or comparative operations.

 

Hope this helps.

[Gleasonator]

Thank you, to all three of you.

 

I just got the little light-bulb over my head and went "Ooooohhhh." I have a much better understanding of the logic behind this now, what is exactly what I was hoping to achieve.

 

I love this site. You guys are awesome.

[chronister]

doing what you did, your pretty much echoing the result twice, it's the same as writing

function add($x,$y)
  {
  $total = $x + $y;
  echo $total;
  }

echo "$total" . add(1,16);

 

 

Nothing against your code timmah, or what your saying... this is for original posters clarification....

 

In your example, $total is not available to the code as it is set inside the function and outside the scope of the operation.

 

So echo $total . add(1,16); essentially is <undefined variable > . add(1,16);

 

$total has no value unless it is set outside the function, or is made available as a global.

 

So to do what you wrote, the function would have to look like this.....

 

 

function add($x,$y)
{
  global $total;

  $total = $x + $y;
  echo $total;
}

echo "$total" . add(1,16);

 

And then, it would not echo 1 + 16, it would echo 17 as $x + $y will perform the arithmetic and set $total to the value of $x + $y.

 

Functions are pretty handy and can be a HEADACHE if you don't understand the scope of variables and such.

 

Hope this makes sense to all...... sorry for posting after it has been marked solved.... just saw this and thought I would give my 1.5 cents

Nate