Logical operators in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of combined logical operators

What is the output of this PHP code snippet?

PHP

<?php
$a = true;
$b = false;
$c = true;
$result = $a && $b || $c;
echo $result ? 'Yes' : 'No';
?>

A 1

B No

C Yes

D Error

💡 Hint

Remember that && has higher precedence than || in PHP.

The expression evaluates as ($a && $b) || $c, which is (true && false) || true, so false || true equals true, printing 'Yes'.

❓ Predict Output

intermediate

Logical operator precedence difference

What is the output of this PHP code?

PHP

<?php
$a = false;
$b = true;
$c = false;
$result = $a or $b and $c;
echo $result ? 'True' : 'False';
?>

A True

B False

C 1

D 0

💡 Hint

Remember that 'and' and 'or' have lower precedence than '=' in PHP.

The assignment happens before 'or' and 'and'. So $result = $a (false), then 'or $b and $c' is evaluated but does not affect $result. So $result is false.

🔧 Debug

advanced

Identify the error in logical expression

Which option will cause a syntax error in PHP when using logical operators?

A $result = true && || false;

B $result = true and false or true;

C $result = true && false || true;

D $result = (true || false) && true;

💡 Hint

Look for missing operands between operators.

Option A has '&& ||' without a value between them, causing a syntax error.

❓ Predict Output

advanced

Output of mixed logical operators with parentheses

What is the output of this PHP code?

PHP

<?php
$a = false;
$b = true;
$c = true;
$result = ($a or $b) and $c;
echo $result ? 'Pass' : 'Fail';
?>

A 0

B Fail

C 1

D Pass

💡 Hint

Parentheses change the order of evaluation.

Inside parentheses: $a or $b is false or true = true. Then true and $c (true) is true, so output is 'Pass'.

🧠 Conceptual

expert

Understanding operator precedence and assignment

Given the code below, what is the value of $result after execution?

PHP

<?php
$result = false;
$flag = true;
$result = $flag && false or true;
?>

A false

B true

C 1

D null

💡 Hint

Remember that '&&' has higher precedence than 'or', but '=' has higher precedence than 'or'.

The expression is evaluated as ($result = ($flag && false)) or true. So $result = false, then 'or true' is evaluated but does not affect $result. So $result remains false.

Practice

1. Which logical operator in PHP returns true only if both conditions are true?

easy

A. && (AND)

B. || (OR)

C. ! (NOT)

D. xor

Solution

1. Step 1: Understand the AND operator

   The AND operator && returns true only if both conditions it connects are true.

2. Step 2: Compare with other operators

   The OR operator || returns true if at least one condition is true, NOT ! negates a condition, and xor returns true if exactly one condition is true.

3. Final Answer:

   && (AND) -> Option A

4. Quick Check:

   AND = both true [OK]

Hint: AND means both must be true to get true [OK]

Common Mistakes:

• Confusing OR (||) with AND (&&)
• Thinking NOT (!) combines two conditions
• Assuming xor behaves like AND

2. Which of the following is the correct syntax for the logical OR operator in PHP?

easy

A. !

B. &&

C. ||

D. and

Solution

1. Step 1: Identify the OR operator syntax

   In PHP, the logical OR operator is written as ||.

2. Step 2: Differentiate from other operators

   && is AND, ! is NOT, and and is a lower precedence alternative but not the common OR operator symbol.

3. Final Answer:

   || -> Option C

4. Quick Check:

   OR = || symbol [OK]

Hint: OR operator is double vertical bars || [OK]

Common Mistakes:

• Using single | instead of ||
• Confusing AND (&&) with OR (||)
• Using 'and' keyword instead of ||

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

$a = true;
$b = false;
if ($a && !$b) {
    echo 'Yes';
} else {
    echo 'No';
}

medium

A. No

B. Yes

C. Syntax Error

D. Nothing

Solution

1. Step 1: Evaluate the NOT operator on $b

   $b is false, so !$b becomes true.

2. Step 2: Evaluate the AND condition

   $a is true and !$b is true, so $a && !$b is true.

3. Final Answer:

   Yes -> Option B

4. Quick Check:

   true AND true = true [OK]

Hint: NOT flips false to true, AND needs both true [OK]

Common Mistakes:

• Ignoring the NOT operator effect
• Assuming false && true is true
• Confusing output strings

4. Find the error in this PHP code snippet:

$x = true;
$y = false;
if ($x || ! $y) {
    echo 'True';
 else {
    echo 'False';
}

medium

A. Missing closing brace for if block

B. Missing semicolon after echo statement

C. Incorrect use of logical OR operator

D. Missing closing parenthesis in if condition

Solution

1. Step 1: Check the if statement syntax

   The if condition has correct parentheses and logical operators.

2. Step 2: Check the braces for if-else blocks

   The if block opens with { but does not have a closing } before the else block starts.

3. Final Answer:

   Missing closing brace for if block -> Option A

4. Quick Check:

   Braces must match for if-else [OK]

Hint: Count opening and closing braces carefully [OK]

Common Mistakes:

• Assuming missing parenthesis causes error
• Thinking logical OR syntax is wrong
• Ignoring missing brace errors

5. Given the variables:

$a = false;
$b = true;
$c = false;

Which expression evaluates to true?
($a || $b) && !$c

hard

A. null

B. false

C. Syntax Error

D. true

Solution

1. Step 1: Evaluate the OR inside parentheses

   $a is false, $b is true, so $a || $b is true.

2. Step 2: Evaluate the NOT operator on $c

   $c is false, so !$c is true.

3. Step 3: Evaluate the AND between results

   true AND true equals true.

4. Final Answer:

   true -> Option D

5. Quick Check:

   (false OR true) AND NOT false = true [OK]

Hint: Evaluate inside parentheses first, then NOT, then AND [OK]

Common Mistakes:

• Ignoring operator precedence
• Misapplying NOT operator
• Assuming OR returns false if one operand is false