Type coercion in operations in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

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

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

PHP

<?php
$a = '5';
$b = 3;
$c = $a + $b;
echo $c;
?>

A 8

B 53

C Error: Unsupported operand types

D 5

💡 Hint

PHP converts strings to numbers when using arithmetic operators.

In PHP, when adding a string containing a number to an integer, the string is converted to an integer. So '5' + 3 becomes 5 + 3 = 8.

❓ Predict Output

intermediate

What does this PHP code output when comparing string and integer?

What is the output of this PHP code snippet?

PHP

<?php
var_dump('10' == 10);
var_dump('10' === 10);
?>

A bool(true) bool(true)

B bool(false) bool(true)

C bool(false) bool(false)

D bool(true) bool(false)

💡 Hint

== compares values after type juggling, === compares both value and type.

The == operator converts '10' to integer 10 and compares values, so true. The === operator checks type and value, string vs integer, so false.

❓ Predict Output

advanced

What is the output of this PHP code with boolean and string addition?

Analyze the following PHP code and select the correct output.

PHP

<?php
$x = true + '2 apples';
echo $x;
?>

A 3

B 1

C 2 apples1

D Error: Unsupported operand types

💡 Hint

PHP converts booleans to integers and strings to numbers when used with + operator.

true converts to 1, '2 apples' converts to 2 (leading number), so 1 + 2 = 3.

❓ Predict Output

advanced

What error or output does this PHP code produce?

What happens when you run this PHP code?

PHP

<?php
$result = 'hello' - 5;
echo $result;
?>

A 0

B Error: Unsupported operand types

C -5

D 5

💡 Hint

PHP converts non-numeric strings to 0 when used in arithmetic.

'hello' converts to 0 because it does not start with a number, so 0 - 5 = -5.

❓ Predict Output

expert

What is the output of this PHP code with array and string addition?

Consider this PHP code. What will it output or error?

PHP

<?php
$a = [1, 2];
$b = '3';
$c = $a + $b;
echo gettype($c);
?>

A string

B Error: Unsupported operand types

C integer

D array

💡 Hint

PHP does not support adding arrays and strings with + operator.

Adding an array and a string with + operator causes a fatal error in PHP: Unsupported operand types.

Practice

1. In PHP, what happens when you add a string containing a number to an integer, like '5' + 3?

easy

A. PHP throws a type error because you can't add string and integer.

B. The result is the string '53' by concatenating '5' and '3'.

C. The string '5' is converted to the number 5, then added to 3, resulting in 8.

D. The operation returns null because of incompatible types.

Solution

1. Step 1: Understand PHP type coercion in addition

   PHP automatically converts strings containing numbers to integers or floats when used in arithmetic operations.

2. Step 2: Apply addition after conversion

   The string '5' becomes the integer 5, then 5 + 3 equals 8.

3. Final Answer:

   8 -> Option C

4. Quick Check:

   '5' + 3 = 8 [OK]

Hint: Strings with numbers convert to numbers in math operations [OK]

Common Mistakes:

• Thinking PHP concatenates strings with + operator
• Expecting a type error on mixed types
• Assuming the result stays a string

2. Which of the following PHP expressions correctly adds a boolean true to an integer 2 and returns 3?

easy

A. (int)'true' + 2

B. true + 2

C. true . 2

D. 'true' + 2

Solution

1. Step 1: Understand boolean to integer conversion

   In PHP, boolean true converts to integer 1 in arithmetic operations.

2. Step 2: Evaluate each option

   (int)'true' + 2: (int)'true' is 0 + 2 = 2 (wrong). 'true' + 2: 'true' converts to 0 + 2 = 2 (wrong). true . 2: concatenation '12' (wrong). true + 2: 1 + 2 = 3 (correct).

3. Final Answer:

   true + 2 -> Option B

4. Quick Check:

   true + 2 = 3 [OK]

Hint: Boolean true acts as 1 in math operations [OK]

Common Mistakes:

• Confusing string 'true' with boolean true
• Using concatenation instead of addition
• Not knowing boolean converts to 1 or 0

3. What is the output of the following PHP code?

$a = '10 apples';
$b = 5;
echo $a + $b;

medium

A. 105

B. 10 apples5

C. Error: Unsupported operand types

D. 15

Solution

1. Step 1: Understand string to number conversion in arithmetic

   PHP converts the string '10 apples' to the number 10 by reading digits from the start until non-digit characters.

2. Step 2: Perform addition

   10 + 5 equals 15, so echo outputs 15.

3. Final Answer:

   15 -> Option D

4. Quick Check:

   '10 apples' + 5 = 15 [OK]

Hint: Strings starting with numbers convert to those numbers in math [OK]

Common Mistakes:

• Expecting string concatenation with +
• Thinking it causes an error
• Assuming the whole string converts to zero

4. Consider this PHP code snippet:

$x = '5 cats';
$y = 3;
$result = $x - $y;
echo $result;

Why might this code produce an unexpected result?

medium

A. PHP converts '5 cats' to 5, so 5 - 3 = 2, which might be unexpected if you expect string behavior.

B. Because subtraction is not defined for strings, it causes a fatal error.

C. The variable $result will be the string '5 cats3' due to concatenation.

D. PHP treats both as strings and outputs '5 cats3'.

Solution

1. Step 1: Analyze subtraction with string and integer

   PHP converts the string '5 cats' to the number 5 for arithmetic operations.

2. Step 2: Calculate the subtraction

   5 - 3 equals 2, so $result is 2, which may surprise if expecting string concatenation or error.

3. Final Answer:

   PHP converts '5 cats' to 5, so result is 2 -> Option A

4. Quick Check:

   '5 cats' - 3 = 2 [OK]

Hint: Subtraction forces string to number conversion [OK]

Common Mistakes:

• Expecting string concatenation with - operator
• Thinking it causes an error
• Assuming result is a string

5. You want to compare two variables in PHP: $a = '0' (string) and $b = false (boolean). Which comparison returns true when using type coercion, and which returns false when checking type strictly?

Choose the correct pair:

hard

A. $a == $b is true; $a === $b is false

B. $a == $b is false; $a === $b is true

C. $a == $b is true; $a === $b is true

D. $a == $b is false; $a === $b is false

Solution

1. Step 1: Understand loose (==) vs strict (===) comparison

   Loose comparison converts types before comparing; strict compares value and type exactly.

2. Step 2: Evaluate comparisons

   Loose: '0' converts to 0, false converts to 0, so 0 == 0 is true. Strict: '0' is string, false is boolean, types differ, so false.

3. Final Answer:

   $a == $b is true; $a === $b is false -> Option A

4. Quick Check:

   '0' == false is true; '0' === false is false [OK]

Hint: Use === to check type and value, == allows type coercion [OK]

Common Mistakes:

• Assuming == checks type strictly
• Thinking '0' and false are always different
• Confusing loose and strict equality