How variables can name other variables

nelsona

Can you explain why $t will work in this code: (i get the value of $var_in[ ])

<?
import_request_variables("gP", "var_");
$i=1;
$b=1;
while ($i<8)
   {
      while($b<7)
  	{
	   $t=$i.$b;
	   echo" <b>IN:</b> $var_in[$t]";
	   echo"<b>OUT:</b> $var_out[$t]";
	   $b++;
	}
      echo" ________________________<BR><BR>";
      $b=1;
      $i++;
   }
?>

Where as $i$b doesn't work?? (I get the values of $i and $b)

<?
import_request_variables("gP", "var_");
$i=1;
$b=1;
while ($i<8)
   {
      while($b<7)
  	{
	   echo" <b>IN:</b> $var_in[$i$b]  ";
	   echo"<b>OUT:</b> $var_out[$i$b]";
	   $b++;
	}
      echo" ________________________<BR><BR>";
      $b=1;
      $i++;
   }
?>

the only thing I can think of is there may be a way in which php sees the variables $i$b being a different vartype than $var_in[]

that being an extreamly wild guess 😕

bradgrafelman

First thing I notice in your code is that you're not handling arrays properly. You shouldn't reference arrays with indeces inside a string unless you use braces, but I've simply found it easy to separate the two, such as:

echo ' <b>IN:</b> ' . $var_in[$i$b] . '  ';

Second thing I notice is that "$i$b" has no meaning to PHP. Actually, it throws an error.

What are you trying to do here? I see the values for $i and $b are both 1, so are you trying to reference the 11th index of $var_in (glueing $i and $b together as if they were a string) ? If so, you need to use a period to concatenate the two together, much like you had when you used the $t variable:

echo ' <b>IN:</b> ' . $var_in[$i.$b] . '  ';

laserlight

You might also consider using for loops:

<?php
import_request_variables("gP", "var_");
for ($i = 1; $i < 8; ++$i)
{
	for ($b = 1; $b < 7; ++$b)
	{
		echo " <b>IN:</b> " . $var_in[$i . $b] . "  "
			. "<b>OUT:</b> " . $var_out[$i . $b];
	}
	echo " ________________________<br \><br \>";
}
?>

nelsona

bradgrafelman wrote:
What are you trying to do here?

yes, I was trying to access 11-16, 21-21 and so on and so on
I see that you had concatenated <b>IN:</b> with the variable where I hadn't
Also, I noticed that you used single quotes, is there any real reason/benefit in doing this over double quotes?

bradgrafelman wrote:
I see the values for $i and $b are both 1, so are you trying to reference the 11th index of $var_in (glueing $i and $b together as if they were a string) ? If so, you need to use a period to concatenate the two together, much like you had when you used the $t variable:
echo ' <b>IN:</b> ' . $var_in[$i.$b] . '  ';

bradgrafelman

You can read more about it on the [man]string[/man] page in the PHP manual, but basically... PHP parses double quoted strings for variables (and special character sequences such as \n, \r, \t, \x00 etc. and replaces them with the appropriate special character), whereas it simply treats single quoted strings as normal strings and does not process them for any such special entities.

Since there was nothing that needed to be parsed in those strings, I used single quotes. Sure, the performance difference is probably negligible, but it's simply a habbit I've gotten into.