in the case shown below both operators generate different values, once TRUE twice FALSE

source code

<?php
function isValid_and($a)
  {
  $valid = true;
  $b = 1;
  
  $valid = $valid and (strlen($a) >= $b);
  
  return $valid;
  }

function isValid_and_($a)
  {
  $valid = true;
  $b = 1;
  
  $valid = $valid && (strlen($a) >= $b);
  
  return $valid;
  }

$a = "";

if (isValid_and($a))
  echo "and - true<br/>";
else
  echo "and - false<br/>";

if (isValid_and_($a))
  echo "&& - true<br/>";
else
  echo "&& - false<br/>";
?>