Comparison pitfalls

Learn the difference between === and == and type coercion pitfalls.

== versus ===

PHP has two equality operators. == does loose comparison: it converts types. === does strict comparison: both value and type must match.

For example, "0" == false returns true because PHP converts the string and compares with false. But "0" === false returns false because a string and a bool are different types. To avoid surprises, prefer ===.

Type coercion pitfalls

Loose comparison makes some surprising conversions. 0 == "abc" returns true because the string becomes 0 when cast to a number. null == false is true and null == 0 is true, but null === false is false.

That is why user input, form submissions and password checks should always use === or !==. Unexpected type conversions can lead to security holes.

Exercise Strict role check

A $role variable is already declared. Write an if with the strict comparison $role === 'admin'; when true, print echo 'welcome'. Do not use ==; use ===.

Show example solution

For strict comparison, write if ($role === 'admin') { ... }.
Example solution:
<?php
$role = 'admin';
// Role check
if ($role === 'admin') {
  echo 'welcome';
}

Test yourself

What is the output of var_dump("0" == false);?
```
var_dump("0" == false);
```
- bool(false)
- NULL
- bool(true)
- string(0)
Show answer

bool(true) — Correct. PHP converts '0' to false, so == returns true.
Match the equality operators

==

Equal (loose)
===

Equal (strict)
!=

Not equal (loose)
!==

Not equal (strict)
Write the strict equality operator
```
var_dump("5" ____ 5);
```
Show answer
```
var_dump("5" === 5);
```

Next lesson: Summary - Conditionals

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