Loose comparison vs strict comparison in PHP - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of loose comparison with different types

What is the output of this PHP code snippet?

PHP

<?php
$a = 0;
$b = '0';
if ($a == $b) {
    echo 'Equal';
} else {
    echo 'Not equal';
}
?>

A Not equal

B Error

C Equal

D 0

💡 Hint

Loose comparison converts types before comparing.

In PHP, the loose comparison operator (==) converts types if needed. Here, integer 0 and string '0' are considered equal.

❓ Predict Output

intermediate

Output of strict comparison with different types

What is the output of this PHP code snippet?

PHP

<?php
$a = 0;
$b = '0';
if ($a === $b) {
    echo 'Equal';
} else {
    echo 'Not equal';
}
?>

A Equal

B Not equal

C Error

D 0

💡 Hint

Strict comparison checks both value and type.

The strict comparison operator (===) checks both value and type. Integer 0 and string '0' are different types, so result is 'Not equal'.

❓ Predict Output

advanced

Loose comparison with boolean and string

What is the output of this PHP code snippet?

PHP

<?php
$a = false;
$b = 'any string';
if ($a == $b) {
    echo 'Equal';
} else {
    echo 'Not equal';
}
?>

A Not equal

B Error

C Equal

D False

💡 Hint

Loose comparison converts string to boolean when compared to boolean.

When comparing boolean to string with loose comparison, the string is converted to boolean. Non-empty string converts to true, so false == true is false, resulting in 'Not equal'.

❓ Predict Output

advanced

Strict comparison with boolean and string

What is the output of this PHP code snippet?

PHP

<?php
$a = false;
$b = 'any string';
if ($a === $b) {
    echo 'Equal';
} else {
    echo 'Not equal';
}
?>

A Equal

B False

C Error

D Not equal

💡 Hint

Strict comparison requires same type and value.

Strict comparison (===) checks type and value. Boolean false and string 'any string' differ in type, so result is 'Not equal'.

🧠 Conceptual

expert

Why does loose comparison between 0 and 'foo' return true?

In PHP, why does the expression (0 == 'foo') evaluate to true?

A Because 'foo' is converted to 0 in numeric context, so 0 == 0 is true.

B Because PHP treats all strings as true in loose comparison.

C Because PHP throws a warning and returns true by default.

D Because 0 is converted to string '0' and compared to 'foo'.

💡 Hint

Think about how PHP converts strings to numbers in loose comparison.

In loose comparison, PHP converts the string 'foo' to 0 because it does not start with a numeric value. Then it compares 0 == 0, which is true.