Logical operators in PHP - Mini Project: Build & Apply

Logical operators

📖 Scenario: You are creating a simple system to check if a person is eligible for a special discount based on their age and membership status.

🎯 Goal: Build a PHP program that uses logical operators to decide if a person qualifies for the discount.

📋 What You'll Learn

Create variables for age and is_member

Create a variable min_age for the minimum age to qualify

Use logical operators and and or to check conditions

Print the eligibility result

💡 Why This Matters

🌍 Real World

Logical operators help decide if multiple conditions are true or false, like checking eligibility for discounts, access, or features.

💼 Career

Understanding logical operators is essential for programming decisions, validations, and controlling program flow in many software jobs.

1

Create initial variables

Create a variable called age and set it to 20. Create a variable called is_member and set it to true.

PHP

<?php
// Create variables 'age' and 'is_member'
// Your code here

Hint

Use $age = 20; and $is_member = true; to create the variables.

2

Add minimum age configuration

Create a variable called min_age and set it to 18.

PHP

<?php
$age = 20;
$is_member = true;
// Create variable 'min_age' and set it to 18
// Your code here

Hint

Use $min_age = 18; to set the minimum age.

3

Check eligibility with logical operators

Create a variable called eligible that is true if age is greater than or equal to min_age and is_member is true. Use the and logical operator.

PHP

<?php
$age = 20;
$is_member = true;
$min_age = 18;
// Create variable 'eligible' using logical operator 'and'
// Your code here

Hint

Use parentheses to compare $age >= $min_age and combine with && $is_member.

4

Print the eligibility result

Print the text Eligible for discount: followed by the value of eligible. Use var_export to show true or false.

PHP

= $min_age) && $is_member;
// Print eligibility result
// Your code here

Hint

Use print("Eligible for discount: " . var_export($eligible, true)); to show the result.

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