Equality & Identity

Part of the Fundamentals section of Coddy's PHP journey — lesson 24 of 71.

PHP provides two ways to check if values are equal: the equality operator (==) and the identity operator (===). Understanding the difference is crucial for writing reliable code.

The equality operator (==) compares values after converting them to the same type. This is called "loose comparison":

<?php
var_dump(5 == "5");    // bool(true) - string converted to number
var_dump(0 == false);  // bool(true) - both become 0
var_dump(1 == true);   // bool(true) - both become 1
?>

The identity operator (===) compares both value and type. No conversion happens, so both must match exactly:

<?php
var_dump(5 === "5");   // bool(false) - int vs string
var_dump(5 === 5);     // bool(true) - same type and value
var_dump(0 === false); // bool(false) - int vs bool
?>

For "not equal" comparisons, use != (loose) or !== (strict):

<?php
var_dump(5 != "5");    // bool(false) - values are equal
var_dump(5 !== "5");   // bool(true) - types differ
?>

As a best practice, prefer === and !== to avoid unexpected type conversion surprises.

Challenge

Easy

Read two values from input: a number (as a string) and an integer.

Use the equality and identity operators to evaluate the following comparisons and print the result of each using var_dump(), each on a new line:

Check if the string value equals the integer using loose comparison (==)
Check if the string value equals the integer using strict comparison (===)
Check if the string value is not equal to the integer using loose comparison (!=)
Check if the string value is not equal to the integer using strict comparison (!==)

Note: Keep the first value as a string (do not cast it). Cast the second value to an integer.

Example:

If the inputs are 42 and 42, the output should be:

bool(true)
bool(false)
bool(false)
bool(true)

Explanation:

"42" == 42 is true (values are equal after type conversion)
"42" === 42 is false (string vs int - different types)
"42" != 42 is false (values are equal)
"42" !== 42 is true (types are different)

Cheat sheet

PHP has two ways to compare values:

Equality operator (==) - loose comparison that converts values to the same type before comparing:

<?php
var_dump(5 == "5");    // bool(true) - string converted to number
var_dump(0 == false);  // bool(true) - both become 0
var_dump(1 == true);   // bool(true) - both become 1
?>

Identity operator (===) - strict comparison that checks both value and type:

<?php
var_dump(5 === "5");   // bool(false) - int vs string
var_dump(5 === 5);     // bool(true) - same type and value
var_dump(0 === false); // bool(false) - int vs bool
?>

Not equal operators:

<?php
var_dump(5 != "5");    // bool(false) - values are equal (loose)
var_dump(5 !== "5");   // bool(true) - types differ (strict)
?>

Best practice: Use === and !== to avoid unexpected type conversion.

Try it yourself

<?php
// Read input
$stringValue = trim(fgets(STDIN));
$intValue = intval(trim(fgets(STDIN)));

// TODO: Write your code below
// Use var_dump() to print the result of each comparison on a new line:
// 1. Loose equality (==)
// 2. Strict equality (===)
// 3. Loose inequality (!=)
// 4. Strict inequality (!==)

?>

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction to PHP

The PHP Language Hello World!Tags and Statements Comments The new line

4Comparison & Logical Operators

Comparison OperatorsEquality & IdentityLogical Operators Part 1 Logical Operators Part 2 Recap - Simple Logic

7Arrays Part 2 - Associative

Intro to Associative Arrays Accessing Values by Key Modifying Values by Key Adding New Key-Value Pairs Check if Key Exists Recap - Key-Value Data Store

10Functions

Declaring & Calling Functions Function Parameters Returning Values Default Parameter Values Type Declarations for Params Return Type Declarations Variable Scope Recap - Creating Reusable Code