Assignment and compound assignment in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of compound assignment with strings

What is the output of this PHP code?

PHP

<?php
$a = "Hello";
$a .= " World";
echo $a;
?>

A World

B HelloWorld

C Hello

D Hello World

💡 Hint

The .= operator adds the right string to the left string.

The .= operator appends the right string to the left string variable. So $a becomes "Hello World".

❓ Predict Output

intermediate

Result of compound assignment with numbers

What is the value of $x after running this PHP code?

PHP

<?php
$x = 10;
$x *= 3 + 2;
echo $x;
?>

A 50

B 15

C 60

D 30

💡 Hint

Remember operator precedence: multiplication and addition.

The expression $x *= 3 + 2 is evaluated as $x *= (3 + 2) = $x *= 5, so $x becomes 10 * 5 = 50.

❓ Predict Output

advanced

Output of chained compound assignments

What is the output of this PHP code?

PHP

<?php
$a = 5;
$b = 10;
$c = 15;
$a += $b -= $c;
echo "$a $b $c";
?>

A 0 -5 15

B 20 -5 15

C 20 25 15

D 5 10 15

💡 Hint

Evaluate inner assignment first, then outer.

First $b -= $c means $b = 10 - 15 = -5. Then $a += $b means $a = 5 + (-5) = 0. $c stays 15.

❓ Predict Output

advanced

Effect of compound assignment with arrays

What error or output does this PHP code produce?

PHP

<?php
$arr = [1, 2, 3];
$arr += [4, 5];
print_r($arr);
?>

A Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 )

B Array ( [0] => 1 [1] => 2 [2] => 3 )

C Fatal error: Unsupported operand types

D Array ( [0] => 1 [1] => 2 [2] => 3 [4] => 5 )

💡 Hint

The += operator for arrays adds elements with keys that do not exist in the left array.

The += operator adds elements from the right array only if the key does not exist in the left array. The right array [4, 5] has keys 0=>4 and 1=>5, both exist in the left array, so nothing is added.

❓ Predict Output

expert

Final value after mixed compound assignments

What is the final value of $result after running this PHP code?

PHP

<?php
$result = 2;
$result *= 3;
$result += 4;
$result /= 2;
$result -= 1;
echo $result;
?>

A 3

B 5

C 4

D 6

💡 Hint

Calculate step by step following the order of operations.

Step 1: $result = 2 Step 2: $result *= 3 → 6 Step 3: $result += 4 → 10 Step 4: $result /= 2 → 5 Step 5: $result -= 1 → 4 Output is 4.

Practice

1. What does the += operator do in PHP?

easy

A. Assigns the right value to the left variable without any operation

B. Multiplies the left variable by the right value

C. Subtracts the right value from the left variable

D. Adds the right value to the left variable and assigns the result to the left variable

Solution

1. Step 1: Understand the += operator

   The += operator adds the value on the right to the variable on the left.

2. Step 2: Assign the result back to the left variable

   It updates the left variable with the new sum.

3. Final Answer:

   Adds the right value to the left variable and assigns the result to the left variable -> Option D

4. Quick Check:

   += means add and assign [OK]

Hint: Think: add right to left and save in left [OK]

Common Mistakes:

• Confusing += with simple assignment =
• Thinking it subtracts or multiplies
• Believing it only adds without assignment

2. Which of the following is the correct syntax to multiply a variable $x by 5 and update it in PHP?

easy

A. $x *= 5;

B. $x =* 5;

C. $x = *5;

D. $x = 5*;

Solution

1. Step 1: Identify the correct compound assignment syntax

   The correct syntax for multiplying and assigning is $x *= 5; with no spaces between * and =.

2. Step 2: Check other options for syntax errors

   The other options have incorrect placement of operators or missing operands.

3. Final Answer:

   $x *= 5; -> Option A

4. Quick Check:

   Use *= for multiply and assign [OK]

Hint: Remember no space: variable *= value [OK]

Common Mistakes:

• Writing =* instead of *= operator
• Adding spaces between * and =
• Placing * or = incorrectly

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

$a = 10;
$a += 5;
$a -= 3;
echo $a;

medium

A. 10

B. 12

C. 8

D. 15

Solution

1. Step 1: Calculate after first operation

   Initially, $a = 10. After $a += 5;, $a becomes 10 + 5 = 15.

2. Step 2: Calculate after second operation

   Then $a -= 3; subtracts 3: 15 - 3 = 12.

3. Final Answer:

   12 -> Option B

4. Quick Check:

   10 + 5 - 3 = 12 [OK]

Hint: Perform operations step-by-step from top to bottom [OK]

Common Mistakes:

• Ignoring the order of operations
• Adding instead of subtracting in second step
• Confusing initial value with final

4. Identify the error in the following PHP code:

$count = 5;
$count +== 3;
echo $count;

medium

A. Variable name is invalid

B. Missing semicolon after first line

C. Using +== instead of +=

D. echo statement syntax error

Solution

1. Step 1: Check the compound assignment operator

   The operator +== is invalid in PHP. The correct operator to add and assign is +=.

2. Step 2: Verify other parts of code

   Semicolons are present, variable name is valid, and echo syntax is correct.

3. Final Answer:

   Using +== instead of += -> Option C

4. Quick Check:

   Compound assignment must be +=, not +== [OK]

Hint: Remember compound operators have one = only [OK]

Common Mistakes:

• Typing two equal signs in compound assignment
• Confusing comparison (==) with assignment (=)
• Assuming +== is valid operator

5. Given the code below, what will be the value of $result after execution?

$x = 4;
$y = 3;
$result = 10;
$result += $x * $y;
$result -= 5;
$result /= 2;

hard

A. 8.5

B. 6.5

C. 10

D. 9

Solution

1. Step 1: Calculate multiplication and addition

   $x * $y = 4 * 3 = 12. Then $result += 12 means 10 + 12 = 22.

2. Step 2: Subtract 5 from $result

   22 - 5 = 17.

3. Step 3: Divide $result by 2

   17 / 2 = 8.5.

4. Step 4: Check options carefully

   8.5 is 8.5, but note the question asks for final value of $result after all operations.

5. Final Answer:

   8.5 -> Option A

6. Quick Check:

   (10 + 4*3 - 5) / 2 = 8.5 [OK]

Hint: Follow order: multiply, add, subtract, divide [OK]

Common Mistakes:

• Ignoring operator precedence
• Doing operations in wrong order
• Dividing before subtracting