Arithmetic operators in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using arithmetic operators?

Consider the following PHP code snippet. What will it output when run?

PHP

<?php
$a = 10;
$b = 3;
echo $a % $b;
?>

A 3

B SyntaxError

C 0

D 1

💡 Hint

The % operator gives the remainder of division.

The expression 10 % 3 calculates the remainder when 10 is divided by 3, which is 1.

❓ Predict Output

intermediate

What is the output of this PHP code with mixed arithmetic?

What will this PHP code print?

PHP

<?php
$x = 5;
$y = 2;
$result = $x ** $y + $x / $y;
echo $result;
?>

A 12.5

B 27

C 27.5

D SyntaxError

💡 Hint

Remember operator precedence: exponentiation before division and addition.

5 ** 2 = 25, 5 / 2 = 2.5, 25 + 2.5 = 27.5.

❓ Predict Output

advanced

What is the output of this PHP code with increment operators?

What will this PHP code output?

PHP

<?php
$a = 3;
$b = $a++ + ++$a;
echo $b;
?>

A 8

B 7

C 6

D SyntaxError

💡 Hint

Remember post-increment returns the value before increment, pre-increment increments first.

Initially, $a=3. $a++ returns 3 then $a becomes 4. ++$a increments $a to 5 then returns 5. So sum is 3 + 5 = 8.

❓ Predict Output

advanced

What error does this PHP code produce?

What error will this PHP code raise when executed?

PHP

<?php
$x = 10 / 0;
echo $x;
?>

A DivisionByZeroError

B Warning: Division by zero

C Fatal error: Uncaught Exception

D No error, outputs 0

💡 Hint

Division by zero is not allowed in PHP 7+ and throws an error.

In PHP 7 and later, dividing by zero throws a DivisionByZeroError exception.

🧠 Conceptual

expert

How many items are in the resulting array after this PHP code runs?

What is the number of elements in the array $arr after running this code?

PHP

<?php
$arr = [];
for ($i = 0; $i < 5; $i++) {
    $arr[$i] = $i * 2;
}
$arr[5] = $arr[2] + $arr[4];
unset($arr[1]);
?>

A 6

B 5

C 4

D 7

💡 Hint

Count elements after adding and removing keys.

Initially 5 elements (keys 0 to 4). Then key 5 is added (total 6). Then key 1 is removed (total 5).

Practice

1. Which arithmetic operator in PHP is used to find the remainder of a division?

easy

A. The subtraction operator (-)

B. The modulus operator (%)

C. The multiplication operator (*)

D. The division operator (/)

Solution

1. Step 1: Understand the modulus operator and compare with other operators

   The modulus operator (%) returns the remainder after division of two numbers. Division (/) returns the quotient, multiplication (*) multiplies, and subtraction (-) subtracts.

2. Final Answer:

   The modulus operator (%) -> Option B

3. Quick Check:

   Remainder = % [OK]

Hint: Remainder means modulus (%) operator [OK]

Common Mistakes:

• Confusing division (/) with modulus (%)
• Using multiplication (*) instead of modulus
• Thinking subtraction (-) gives remainder

2. Which of the following is the correct syntax to add two variables $a and $b in PHP?

easy

A. $sum = $a / $b;

B. $sum = $a - $b;

C. $sum = $a * $b;

D. $sum = $a + $b;

Solution

1. Step 1: Identify the addition operator and check the syntax correctness

   In PHP, the plus sign (+) adds two numbers or variables. The syntax $sum = $a + $b; correctly assigns the sum of $a and $b to $sum.

2. Final Answer:

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

3. Quick Check:

   Addition uses + [OK]

Hint: Use + for addition between variables [OK]

Common Mistakes:

• Using - instead of + for addition
• Using * or / which are multiplication/division
• Missing semicolon at end

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

$x = 10;
$y = 3;
echo $x % $y;

medium

A. 1

B. 3

C. 0

D. Syntax Error

Solution

1. Step 1: Calculate the modulus of 10 and 3 and understand the output of echo $x % $y;

   10 divided by 3 is 3 with a remainder of 1. The modulus operator (%) returns the remainder, so output is 1.

2. Final Answer:

   1 -> Option A

3. Quick Check:

   10 % 3 = 1 [OK]

Hint: Modulus gives remainder, 10 % 3 = 1 [OK]

Common Mistakes:

• Confusing modulus with division result
• Expecting 3 instead of remainder 1
• Syntax errors from missing semicolon

4. Identify the error in this PHP code snippet:

$a = 5;
$b = 0;
echo $a / $b;

medium

A. Incorrect use of multiplication operator

B. Syntax error due to missing semicolon

C. Division by zero error

D. No error, outputs 0

Solution

1. Step 1: Analyze the division operation and check for syntax correctness

   Dividing any number by zero is not allowed and causes an error in PHP. Semicolons are present; multiplication operator is not used here.

2. Final Answer:

   Division by zero error -> Option C

3. Quick Check:

   Division by zero causes error [OK]

Hint: Never divide by zero to avoid errors [OK]

Common Mistakes:

• Ignoring division by zero error
• Thinking output is 0
• Confusing syntax error with runtime error

5. You want to calculate the total cost after applying a 15% discount on a price stored in $price. Which PHP expression correctly calculates the discounted price?

hard

A. $discounted = $price - ($price * 0.15);

B. $discounted = $price + ($price * 0.15);

C. $discounted = $price * 0.15;

D. $discounted = $price / 0.15;

Solution

1. Step 1: Calculate the discount amount and subtract discount from original price

   Multiply the price by 0.15 to get 15% of the price. Subtract the discount amount from the original price to get the discounted price.

2. Final Answer:

   $discounted = $price - ($price * 0.15); -> Option A

3. Quick Check:

   Discounted price = price - 15% price [OK]

Hint: Subtract 15% of price for discount [OK]

Common Mistakes:

• Adding discount instead of subtracting
• Using only 15% value without subtracting
• Dividing price by 0.15 incorrectly