Comparison operators (loose and strict) in PHP

Introduction

Comparison operators help you check if two values are equal or different. Loose and strict comparisons decide how carefully PHP checks the values.

Checking if a user input matches a stored password (strict check).

Comparing numbers and strings that might look similar (loose check).

Deciding if two variables hold the same value and type (strict check).

Filtering data where type differences don't matter (loose check).

Syntax

PHP

$a == $b  // loose equality
$a === $b // strict equality
$a != $b  // loose inequality
$a !== $b // strict inequality

Loose comparison (==, !=) converts types if needed before comparing.

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

Examples

Loose equality says true because '5' and 5 are equal after type conversion. Strict equality says false because one is integer and the other is string.

PHP

$a = 5;
$b = '5';
var_dump($a == $b);  // true
var_dump($a === $b); // false

Loose equality treats 0 and false as equal. Strict equality sees different types and returns false.

PHP

$x = 0;
$y = false;
var_dump($x == $y);  // true
var_dump($x === $y); // false

Loose equality treats null and empty string as different, so returns false. Strict equality checks type and finds them different.

PHP

$m = null;
$n = '';
var_dump($m == $n);  // false
var_dump($m === $n); // false

Sample Program

This program compares variables using loose and strict operators and prints which comparisons are true or false.

PHP

<?php
$a = 10;
$b = '10';
$c = 20;

if ($a == $b) {
    echo "$a == $b is true\n";
} else {
    echo "$a == $b is false\n";
}

if ($a === $b) {
    echo "$a === $b is true\n";
} else {
    echo "$a === $b is false\n";
}

if ($a != $c) {
    echo "$a != $c is true\n";
} else {
    echo "$a != $c is false\n";
}

if ($a !== $b) {
    echo "$a !== $b is true\n";
} else {
    echo "$a !== $b is false\n";
}
?>

Important Notes

Loose comparison can cause unexpected results if types differ, so use strict comparison when type matters.

Strict comparison is safer for checking exact matches, like passwords or IDs.

Summary

Use == and != for loose comparison that converts types.

Use === and !== for strict comparison that checks type and value.

Strict comparison helps avoid bugs from type juggling.

Practice

1. Which PHP comparison operator checks both value and type strictly?

easy

A. ===

B. ==

C. !=

D. <>

Solution

1. Step 1: Understand loose vs strict comparison

   Loose comparison (==) checks value after type conversion, strict (===) checks value and type exactly.

2. Step 2: Identify operator that checks type and value

   The operator === compares both type and value strictly without conversion.

3. Final Answer:

   === -> Option A

4. Quick Check:

   Strict comparison = === [OK]

Hint: Use === to compare type and value exactly [OK]

Common Mistakes:

• Confusing == with ===
• Thinking != checks type
• Using <> instead of !=

2. Which of the following is the correct syntax for a strict inequality check in PHP?

easy

A. !=

B. !==

C. <>

D. !===

Solution

1. Step 1: Recall PHP strict inequality operator

   Strict inequality operator in PHP is !== which checks both type and value are not equal.

2. Step 2: Identify correct syntax

   !== is valid syntax; !=== is invalid and others are loose inequality.

3. Final Answer:

   !== -> Option B

4. Quick Check:

   Strict inequality = !== [OK]

Hint: Use !== for strict not equal check [OK]

Common Mistakes:

• Using !=== which is invalid
• Confusing != with !==
• Using <> for strict inequality

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

$a = 0;
$b = '0';
var_dump($a == $b);
var_dump($a === $b);

medium

A. bool(true) bool(false)

B. bool(false) bool(true)

C. bool(true) bool(true)

D. bool(false) bool(false)

Solution

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

   0 (int) and '0' (string) are equal after type conversion, so $a == $b is true.

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

   Types differ (int vs string), so $a === $b is false.

3. Final Answer:

   bool(true) bool(false) -> Option A

4. Quick Check:

   Loose == true, Strict === false [OK]

Hint: Remember === checks type too, == converts types [OK]

Common Mistakes:

• Assuming both comparisons return true
• Ignoring type difference in strict check
• Confusing output order

4. Find the error in this PHP code snippet:

$x = 5;
if ($x = '5') {
  echo 'Equal';
} else {
  echo 'Not equal';
}

medium

A. Missing semicolon after echo

B. Using strict comparison (===) instead of loose

C. Assignment (=) used instead of comparison (==)

D. Variable $x is not defined

Solution

1. Step 1: Identify operator in if condition

   The condition uses = which assigns '5' to $x instead of comparing.

2. Step 2: Understand effect of assignment in condition

   Assignment returns the assigned value, which is truthy, so 'Equal' always prints regardless of original $x.

3. Final Answer:

   Assignment (=) used instead of comparison (==) -> Option C

4. Quick Check:

   Use == for comparison, not = [OK]

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

Common Mistakes:

• Confusing = with == in conditions
• Thinking strict comparison is error here
• Ignoring that assignment returns value

5. You want to filter an array to keep only elements that are exactly integer 0, excluding string '0'. Which comparison operator should you use in PHP?

hard

A. ==

B. !==

C. !=

D. ===

Solution

1. Step 1: Understand filtering requirement

   We want to keep only elements that are integer 0, not string '0'. So type matters.

2. Step 2: Choose operator that checks type and value

   Strict equality (===) checks both value and type, so it excludes string '0'.

3. Final Answer:

   === -> Option D

4. Quick Check:

   Strict equality === filters exact type and value [OK]

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

Common Mistakes:

• Using == which allows type conversion
• Using != or !== which exclude 0
• Ignoring type difference in filtering