Boolean type behavior in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assign a boolean true value to the variable.

PHP

<?php
$flag = [1];
var_dump($flag);

Drag options to blanks, or click blank then click option'

ATrue

B"true"

Ctrue

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using "True" with uppercase T which is not recognized as boolean.

Using quotes around true, making it a string instead of boolean.

The correct boolean value in PHP is true (all lowercase). It represents the boolean true.

2fill in blank

medium

Complete the code to check if the variable is boolean using the correct function.

PHP

<?php
$value = false;
if ([1]($value)) {
    echo "It is boolean.";
} else {
    echo "It is not boolean.";
}

Drag options to blanks, or click blank then click option'

Ais_bool

Bis_true

Cboolval

Dis_boolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_boolean which does not exist in PHP.

Using boolval which converts to boolean but does not check type.

The function is_bool() checks if a variable is of boolean type in PHP.

3fill in blank

hard

Fix the error in the code to correctly convert a string to boolean.

PHP

<?php
$input = "false";
$boolValue = [1]($input);
var_dump($boolValue);

Drag options to blanks, or click blank then click option'

A(boolval)

Bbool

Cbooleanval

Dboolval

Attempts:

3 left

💡 Hint

Common Mistakes

Using bool as a function which causes error.

Using booleanval which does not exist.

The function boolval() converts a value to boolean in PHP. Casting with (bool) is also valid but not listed here.

4fill in blank

hard

Fill both blanks to create an array with keys as words and values as their boolean check.

PHP

<?php
$words = ["yes", "no", "true", "false"];
$result = [[1] => [2] for [1] in $words];

Drag options to blanks, or click blank then click option'

A"word"

Bboolval($word)

C$word

Dis_bool($word)

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the key which makes it a string literal.

Using is_bool which checks type but does not convert.

The key should be the variable $word and the value should be the boolean conversion boolval($word).

5fill in blank

hard

Fill all three blanks to create a filtered array with words whose boolean value is true.

PHP

<?php
$words = ["", "0", "1", "true"];
$filtered = array_filter($words, function($[1]) {
    return [2]($[3]);
});

Drag options to blanks, or click blank then click option'

Aitem

Bboolval

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inside and outside the function.

Using a function other than boolval for conversion.

The variable name in the function is $word. The function boolval converts it to boolean for filtering.

Practice

1. In PHP, which of the following values is considered true when converted to a boolean?

easy

A. The string "false"

B. The integer 0

C. An empty string ""

D. Any non-zero number

Solution

1. Step 1: Understand PHP boolean conversion rules

   In PHP, zero (0), empty string (""), and the string "0" are considered false. Any non-zero number is true.

2. Step 2: Evaluate each option

   Any non-zero number is a non-zero number, so it converts to true. Options B and C are false values. The string "false" is a non-empty string, so it is true, but "false" as a string is not false boolean.

3. Final Answer:

   Any non-zero number -> Option D

4. Quick Check:

   Non-zero number = true [OK]

Hint: Non-zero numbers are true; zero and empty strings are false [OK]

Common Mistakes:

• Thinking string "false" is boolean false
• Assuming zero is true
• Confusing empty string with true

2. Which of the following is the correct way to explicitly cast a variable $var to boolean in PHP?

easy

A. $bool = boolean($var);

B. $bool = bool($var);

C. $bool = (bool) $var;

D. $bool = to_bool($var);

Solution

1. Step 1: Recall PHP casting syntax

   PHP uses (bool) or (boolean) to cast variables to boolean type. The function bool() or boolean() does not exist.

2. Step 2: Check each option

   $bool = (bool) $var; uses (bool) casting which is correct. Options B, C, and D use invalid function calls.

3. Final Answer:

   $bool = (bool) $var; -> Option C

4. Quick Check:

   Use (bool) for casting [OK]

Hint: Use (bool) before variable to cast to boolean [OK]

Common Mistakes:

• Using non-existent functions like bool()
• Confusing casting with function calls
• Using wrong keywords like boolean()

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

$a = 0;
$b = "0";
$c = "false";
$d = [];

echo (int)(bool)$a . "," . (int)(bool)$b . "," . (int)(bool)$c . "," . (int)(bool)$d;

medium

A. 0,0,1,0

B. 0,1,1,0

C. 0,0,0,0

D. 1,1,1,1

Solution

1. Step 1: Convert each variable to boolean

   $a = 0 is false, $b = "0" is false, $c = "false" is a non-empty string so true, $d = [] (empty array) is false.

2. Step 2: Cast booleans to int and concatenate

   False becomes 0, true becomes 1. So output is "0,0,1,0".

3. Final Answer:

   0,0,1,0 -> Option A

4. Quick Check:

   False=0, True=1 [OK]

Hint: Empty, zero, and "0" are false; non-empty strings true [OK]

Common Mistakes:

• Assuming string "false" is false boolean
• Thinking empty array is true
• Mixing string and boolean conversion

4. Consider this PHP code snippet:

$value = "";
if ($value == true) {
    echo "Yes";
} else {
    echo "No";
}

Why does it output "No" and how to fix it to check if $value is truthy?

medium

A. Because empty string is false; use (bool)$value in if condition

B. Because == does loose comparison; use === true to fix

C. Because $value is string; cast to int before comparison

D. Because PHP treats all strings as false; use strlen() instead

Solution

1. Step 1: Understand why empty string is false

   In PHP, empty string "" is considered false in boolean context, so if ($value == true) fails.

2. Step 2: Fix by casting to boolean in condition

   Use if ((bool)$value) or simply if ($value) to check truthiness correctly.

3. Final Answer:

   Because empty string is false; use (bool)$value in if condition -> Option A

4. Quick Check:

   Empty string = false; cast to bool to check [OK]

Hint: Empty string is false; cast variable to bool in conditions [OK]

Common Mistakes:

• Using == true instead of casting
• Assuming all strings are true
• Trying to cast string to int unnecessarily

5. You want to filter an array in PHP to keep only truthy values (non-empty, non-zero, etc.). Which code correctly uses boolean behavior to achieve this?

$arr = [0, 1, "", "hello", false, true, null, [], [1]];
$filtered = array_filter($arr, function($v) {
    // What to put here?
});
print_r($filtered);

hard

A. return $v == true;

B. return (bool)$v;

C. return $v === true;

D. return !empty($v);

Solution

1. Step 1: Understand array_filter callback

   The callback should return true for values to keep. Casting to (bool) returns true for all truthy values.

2. Step 2: Compare options

   return (bool)$v; casts to boolean correctly. return $v == true; uses loose comparison which may include unwanted values. return $v === true; keeps only true boolean, excluding truthy values. return !empty($v); excludes some truthy values like true boolean but empty arrays are false.

3. Final Answer:

   return (bool)$v; -> Option B

4. Quick Check:

   Cast to bool to filter truthy values [OK]

Hint: Use (bool) cast in filter callback to keep truthy values [OK]

Common Mistakes:

• Using strict === true excludes truthy but non-true values
• Using == true includes unwanted falsy values
• Using empty() excludes some truthy values