$var = $value; // ok
$var = "$value"; // ok, but double quotes are not necessary
$var = '$value'; // will not work (single quotes will not allow parsing)

('.' the period adds/connects variables, functions, etc. together.
Oftentimes programmers will leave spaces around the ' . ' to make
things easier to read.)

$var = 'This is the ' . $value . ' of things.'; // ok - preferred
technique
$var = "This is the $value of things."; // ok, but harder to read/debug
$var = 'This is the $value of things.'; // will not parse $value
$var = This is the $value of things.; // error

$var = $array['name']; // ok, generally the preferred technique
$var = $array["name"]; // ok, but why use double quotes if they are not
necessary?
$var = "$array[name]"; // ok, but harder to read/debug - poor coding
style

$var = 'Name: ' . $array['name']; // ok - preferred technique
$var = "Name: $array[name]"; // ok, but harder to read/debug - poor
coding style
$var = "Name: $array["name"]"; // error
$var = "Name: $array['name']"; // error

exampleFunction($value); // ok
exampleFunction("$value"); // ok, but double quotes are not necessary
exampleFunction('$value'); // will not parse $value

$line = $result['name'] . ' ' . $result['last_name']; // ok - easy to
read/debug
$line = $result["name"] . ' ' . $result["last_name"]; // ok, but why
use double quotes if they are not necessary?
$line = "$result[name] $result[last_name]"; // ok - but much harder to
read/debug - poor coding style

$line = $result['name'] . ' ' . doSomething($result['last_name']); //
ok - preferred method (using a function)

if (empty($_POST['action'])) {
  $action = 'default';
} else {
  $action = $_POST['action'];
}

$action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

function safeQuery($query='')
{
  global $db;
  if (!$query) return false; 
  return mysql_query($query, $db->link);
}

// returns an array of records
function fetchArray($query='')
{
  if ($result = safeQuery($query)) {
      if (mysql_num_rows($result) > 0) {
          while ($arr = mysql_fetch_assoc($result)) $rows[] = $arr;
          return $rows;
      }
  }
  return false;
}

// returns a single record
function fetchRecord($query='')
{ 
  if ($row = safeQuery($query)) {
      if (mysql_num_rows($row) > 0) {
          return mysql_fetch_assoc($row);
      }
  }
  return false;
}

$results = fetchArray("SELECT id,field1 FROM records");

// sample output results
if (!$results) {
  echo 'No results.';
} else {
  // loop the data
  foreach ($results as $result) {
      echo $result['id'] . ' ' . $result['field1'];
  }
}