Inverting Statements in If-Else

Consider the following code:

php<?php
  if ($num > 0 and $num < 5) {
    echo '+++';
  } else {
    echo '---';
  }
?>

Let's invert the condition from the given code, that is, turn it into its opposite. The opposite condition will be as follows:

php<?php
  if ($num <= 0 or $num >= 5) {
    echo '+++';
  } else {
    echo '---';
  }
?>

As you can see, inverting a condition requires some thought. It is much easier to use the ! operator, which represents a logical NOT. Using this operator, we just need to put an exclamation mark before the initial condition - and it will invert itself:

php<?php
  if ( !($num > 0 and $num < 5) ) {
    echo '+++';
  } else {
    echo '---';
  }
?>

php<?php
  if ($num1 >= 0 or $num2 <= 10) {
    echo '+++';
  } else {
    echo '---';
  }
?>