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Comparison Operators

    In previous page, you have seen difference between = (simple assignment) operator and == (equal to) operator. You have been also introduced with other comparison operators. Comparison operators, as their name implies, allow you to compare two values. In loose comparison (== equal to, and != not equal to), type juggling happens, that is when a number or numeric string is compared with other data-types, those are automatically type-casted to numeric data-type.

<?php
  $abc = 5; $xyz = "5";   // variable $abc is integer, whereas $xyz is string.
  var_dump( $abc == $xyz );   // equal to operator checks loose comparison, outputs bool(true)
  echo '<br />';
  var_dump( $abc === $xyz );   // identical to operator checks strict comparison, outputs bool(false)
  echo '<br />';

  var_dump( $abc != $xyz );   // not equal to operator checks loose comparison, outputs bool(false)
  echo '<br />';
  var_dump( $abc !== $xyz );   // not identical to operator checks strict comparison, outputs bool(true)
  echo '<br />';
?>

    === (identical to) and !== (not identical to) operators compare not only the values of two literals (or variables/constants), but they also compare the data-types of these two literals (or variables/constants). == (equal to) operator loosely compares two literals or two variables/constants. Let's elaborate those comparison operators in following examples:

<?php
  var_dump( 5.5 == "5.5" ); // Outputs bool(true)
  echo '<br />'; var_dump( null == "" ); // Outputs bool(true)
  echo '<br />'; var_dump( false == "" ); // Outputs bool(true)
  echo '<br />'; var_dump( 0 == false ); // Outputs bool(true)
  echo '<br />'; var_dump( 0 == null ); // Outputs bool(true)
  echo '<br />'; var_dump( 0 == "0" ); // Outputs bool(true)
  echo '<br />'; var_dump( 7 == "07" ); // Outputs bool(true)
  echo '<br />'; var_dump( 7 == "+07" ); // Outputs bool(true)
  echo '<br />'; var_dump( 7 == "    07" ); // Outputs bool(true)
  echo '<br />'; var_dump( 70 == 70.00 ); // Outputs bool(true)
  echo '<br />'; var_dump( 700 == "7e2" ); // Outputs bool(true)
  echo '<br />'; var_dump( 2 == true ); // Outputs bool(true)
  echo '<br />'; var_dump( "xyz" == true ); // Outputs bool(true)
?>

    The each of above example is known as 'FALSE POSITIVE' because all of these when loosely compared, output bool(true), but when they are strictly compared with === (identical to) operator, all of these will output bool(false). Any string that contains the letter E (case insensitive) bounded by numbers will be seen as a number expressed in scientific notation. This can produce unexpected results, as described in above example.

    Following four examples also output bool(true) before PHP 7.1.0 and neither E_NOTICE nor E_WARNING was raised. You will learn more about different types of ERRORS in later topics. In older versions of PHP, when a string data-type is loosely compared with integer or float data-types, the string is evaluated after type-juggling.

<?php var_dump( 0 == "" ); // Outputs bool(false) ?><br />

<?php var_dump( "0" == "" ); // Outputs bool(false) ?><br />

<?php var_dump( 0 == "abc" ); // Outputs bool(false) ?><br />

<?php var_dump( 3 == "3 sparrows" ); // Outputs bool(false) ?><br />

    However, now in latest version of PHP, when a number is compared with a string data-type, and the string literal is not numeric string, then the number is type-casted into string data-type and then comparison happens. Therefore, you should carefully TEST and EXAMINE your PHP codes when hosting your CMS or WEBSITE on a SERVER having an older version of PHP. Other comparison operators are self-explanatory, and are described hereinbelow:

<?php var_dump( 5 < "6" ); // less than operator, outputs bool(true) ?><br />

<?php var_dump( 6 > "4" ); // greater than operator, outputs bool(true) ?><br />

<?php var_dump( 5 <= "6" ); // less than or equal to operator, outputs bool(true) ?><br />

<?php var_dump( 6 >= "4" ); // greater than or equal to operator, outputs bool(true) ?><br />

<?php var_dump( 6 <> 4 ); // less than or greater than (not equal to) operator, outputs bool(true) ?><br />

<?php var_dump( 6 <=> 4 ); // spaceship operator, outputs int(1) ?><br />

<?php var_dump( 6 <=> 6 ); // spaceship operator, outputs int(0) ?><br />

<?php var_dump( 4 <=> 6 ); // spaceship operator, outputs int(-1) ?><br />

<?php var_dump( [] == "" ); // Outputs bool(false) ?><br />

Operator Precedence & Associativity

    Following table shows the HIGHER level of precedence of operators at the top, and LOWER level of precedence below these operators. It means that ** (exponent) operator has higher precedence over other operators. Remember basic arithmetic from school? These work just like those.

Arithmetic Operators

    The unary + (identity) and - (negation) are prefix to any variable name or a literal. Also, ++ (increment) and -- (decrement) can be either prefix or postfix to any variable name or a literal. Increment and decrement operators are used to increase or decrease, respectively the value of a variable name by 1 (one).