String concatenation operator in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using concatenation?

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

PHP

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

A Hello World!

B HelloWorld!

C Hello World

D Hello.World!

💡 Hint

Remember the dot (.) operator joins strings exactly as written.

The dot operator concatenates strings exactly. Here, $a and $b are joined with a space and an exclamation mark, producing 'Hello World!'.

❓ Predict Output

intermediate

What does this PHP code output with mixed concatenation and addition?

Look at this PHP code. What will it output?

PHP

<?php
$x = 5;
$y = "10";
echo $x + $y . " apples";
?>

A 510 apples

B 15 apples

C 5 apples

D TypeError

💡 Hint

PHP converts strings to numbers when using + operator.

The + operator adds numbers, so $y is converted from "10" to 10. Then 5 + 10 = 15. The dot concatenates '15' with ' apples'.

🔧 Debug

advanced

Which option causes a syntax error in PHP string concatenation?

Identify which code snippet will cause a syntax error when run.

A <?php echo "Hello" .+ "World"; ?>

B <?php echo "Hello" + "World"; ?>

C <?php echo "Hello" . " " . "World"; ?>

D <?php echo "Hello" . "World"; ?>

💡 Hint

Check the operator symbols carefully.

Option A uses '.+' which is not a valid operator in PHP, causing a syntax error.

❓ Predict Output

advanced

What is the output of this PHP code with concatenation assignment?

What will this PHP code print?

PHP

<?php
$str = "Good";
$str .= " Morning";
$str .= "!";
echo $str;
?>

A Good . Morning!

B GoodMorning!

C Good Morning

D Good Morning!

💡 Hint

The '.=' operator adds to the existing string.

The '.=' operator appends strings. So $str becomes 'Good Morning!' after both concatenations.

🧠 Conceptual

expert

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

What is the count of elements in the array after this code executes?

PHP

<?php
$arr = [];
$arr['a'] = 'Hello';
$arr['b'] = 'World';
$arr['a'] .= ' PHP';
?>

A 1

B 3

C 2

D 0

💡 Hint

Appending to an existing key does not add new elements.

The array has keys 'a' and 'b'. The '.=' operator appends to the value at 'a' but does not add new keys. So total elements remain 2.

Practice

1. What does the dot (.) operator do in PHP?

easy

A. Joins two strings together

B. Adds two numbers

C. Compares two strings

D. Divides two numbers

Solution

1. Step 1: Understand the dot operator usage

   In PHP, the dot operator is used to join or concatenate strings.

2. Step 2: Differentiate from other operators

   It does not perform arithmetic or comparison; it only combines strings.

3. Final Answer:

   Joins two strings together -> Option A

4. Quick Check:

   Dot operator = string join [OK]

Hint: Dot (.) always joins strings in PHP [OK]

Common Mistakes:

• Confusing dot with plus (+) for addition
• Thinking dot compares strings
• Using dot for division

2. Which of the following is the correct way to concatenate two strings $a and $b in PHP?

easy

A. $a + $b

B. $a . $b

C. $a & $b

D. $a * $b

Solution

1. Step 1: Identify the concatenation operator

   PHP uses the dot (.) operator to join strings, so $a . $b is correct.

2. Step 2: Check other operators

   Plus (+) adds numbers, ampersand (&) is bitwise AND, and asterisk (*) is multiplication.

3. Final Answer:

   $a . $b -> Option B

4. Quick Check:

   Dot (.) concatenates strings [OK]

Hint: Use dot (.) to join strings, not plus (+) [OK]

Common Mistakes:

• Using + instead of . for strings
• Using & or * operators mistakenly
• Missing the dot operator

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

$greeting = "Hello";
$name = "Alice";
echo $greeting . ", " . $name . "!";

medium

A. Hello,Alice!

B. Hello Alice!

C. Hello, Alice!

D. Hello . , . Alice . !

Solution

1. Step 1: Analyze string concatenation

   The code joins "Hello", ", ", "Alice", and "!" using the dot operator.

2. Step 2: Combine strings step-by-step

   "Hello" . ", " = "Hello, " and then "Hello, " . "Alice" = "Hello, Alice" and finally "Hello, Alice" . "!" = "Hello, Alice!"

3. Final Answer:

   Hello, Alice! -> Option C

4. Quick Check:

   Concatenate with dot = Hello, Alice! [OK]

Hint: Dot joins strings exactly as written [OK]

Common Mistakes:

• Missing spaces inside strings
• Expecting plus (+) to work
• Confusing output with literal dots

4. Find the error in this PHP code:

$first = "Good";
$second = "Morning";
echo $first + " " + $second;

medium

A. Using double quotes incorrectly

B. Missing semicolon after echo

C. Variables not declared

D. Using + instead of . for string concatenation

Solution

1. Step 1: Identify operator misuse

   The code uses + to join strings, but PHP requires the dot (.) operator for concatenation.

2. Step 2: Confirm other syntax is correct

   Semicolons are present, variables declared, and quotes are correct.

3. Final Answer:

   Using + instead of . for string concatenation -> Option D

4. Quick Check:

   Use dot (.) not plus (+) for strings [OK]

Hint: Remember: + is for numbers, . is for strings [OK]

Common Mistakes:

• Using + to join strings
• Thinking + works like in JavaScript
• Ignoring PHP string rules

5. You want to create a full name string from $firstName and $lastName with a space between them. Which code correctly does this in PHP?

hard

A. $fullName = $firstName . " " . $lastName;

B. $fullName = $firstName + " " + $lastName;

C. $fullName = $firstName . $lastName;

D. $fullName = '$firstName $lastName';

Solution

1. Step 1: Understand string concatenation with space

   To join first and last names with a space, you must add " " explicitly between them using dot operators.

2. Step 2: Evaluate each option

   A misses the space, B uses + which is invalid for strings, D uses single quotes so variables are not interpolated.

3. Final Answer:

   $fullName = $firstName . " " . $lastName; -> Option A

4. Quick Check:

   Dot with space string joins names correctly [OK]

Hint: Add space as " " between strings with dot [OK]

Common Mistakes:

• Forgetting space between names
• Using + instead of .
• Assuming variables parse inside single quotes