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.

Practice

1. What is the main difference between == and === in PHP?

easy

A. == compares values after type conversion, === compares value and type exactly

B. == compares only types, === compares only values

C. == is used for assignment, === is used for comparison

D. == compares memory addresses, === compares values

Solution

1. Step 1: Understand loose comparison

   Loose comparison (==) converts types if needed and then compares values.

2. Step 2: Understand strict comparison

   Strict comparison (===) checks both value and type without conversion.

3. Final Answer:

   == compares values after type conversion, === compares value and type exactly -> Option A

4. Quick Check:

   Loose == vs Strict === = == compares values after type conversion, === compares value and type exactly [OK]

Hint: Remember: === means exactly equal type and value [OK]

Common Mistakes:

• Thinking == compares types only
• Confusing assignment (=) with comparison (==)
• Assuming === converts types before comparing

2. Which of the following is the correct syntax for strict comparison in PHP?

easy

A. $a = $b;

B. $a !== $b;

C. $a == $b;

D. $a === $b;

Solution

1. Step 1: Identify strict comparison operator

   Strict comparison uses three equal signs: ===.

2. Step 2: Check syntax correctness

   $a === $b; is valid syntax for strict comparison.

3. Final Answer:

   $a === $b; -> Option D

4. Quick Check:

   Strict comparison syntax = $a === $b; [OK]

Hint: Use three equal signs for strict comparison [OK]

Common Mistakes:

• Typing == instead of ===
• Using = which is assignment, not comparison
• Confusing == (loose) with === (strict)

3. What will be the output of the following PHP code?

$a = 0;
$b = '0';
if ($a == $b) {
    echo 'Equal';
} else {
    echo 'Not Equal';
}
if ($a === $b) {
    echo ' Strictly Equal';
} else {
    echo ' Not Strictly Equal';
}

medium

A. Equal Strictly Equal

B. Not Equal Strictly Equal

C. Equal Not Strictly Equal

D. Not Equal Not Strictly Equal

Solution

1. Step 1: Evaluate loose comparison ($a == $b)

   $a is integer 0, $b is string '0'. Loose comparison converts types, so 0 == '0' is true, prints 'Equal'.

2. Step 2: Evaluate strict comparison ($a === $b)

   Strict comparison checks type and value. Integer 0 !== string '0', so false, prints ' Not Strictly Equal'.

3. Final Answer:

   Equal Not Strictly Equal -> Option C

4. Quick Check:

   0 == '0' true, 0 === '0' false = Equal Not Strictly Equal [OK]

Hint: Loose ignores type, strict checks type too [OK]

Common Mistakes:

• Assuming strict comparison returns true for 0 and '0'
• Confusing output order
• Ignoring spaces in echoed strings

4. Find the error in this PHP code snippet:

$x = '10';
if ($x = 10) {
    echo 'Match';
} else {
    echo 'No Match';
}

medium

A. Using assignment (=) instead of comparison (==) in if condition

B. Missing semicolon after echo statement

C. Using double quotes instead of single quotes

D. Variable $x is not defined

Solution

1. Step 1: Check if condition operator

   The condition uses = which assigns 10 to $x instead of comparing.

2. Step 2: Understand effect of assignment in if

   Assignment returns 10 (truthy), so 'Match' always prints, ignoring original $x value.

3. Final Answer:

   Using assignment (=) instead of comparison (==) in if condition -> Option A

4. Quick Check:

   Assignment in if condition = Using assignment (=) instead of comparison (==) in if condition [OK]

Hint: Use == or === for comparison, not = [OK]

Common Mistakes:

• Confusing = with == in conditions
• Thinking missing semicolon causes error here
• Assuming quotes affect comparison operator

5. You want to check if a user input variable $input is exactly the integer 0 (zero) and not a string '0' or other falsy value. Which condition is the best to use?

hard

A. if ($input == 0)

B. if ($input === 0)

C. if ($input != 0)

D. if ($input !== 0)

Solution

1. Step 1: Understand the requirement

   We want to check if $input is integer 0 exactly, not string '0' or other falsy values.

2. Step 2: Choose strict comparison

   == allows type conversion, so string '0' == 0 is true, which is not desired. === checks type and value strictly.

3. Final Answer:

   if ($input === 0) -> Option B

4. Quick Check:

   Exact type and value check = if ($input === 0) [OK]

Hint: Use === to check exact type and value [OK]

Common Mistakes:

• Using == and getting true for string '0'
• Using != or !== which check for inequality
• Ignoring type differences in comparisons