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String concatenation

PHP course · Beginner · Lesson 32/116

Learn to concatenate strings with . and the common mistakes around it.

Joining with . and .=

In PHP you join two strings with the . (dot) operator. "Hello" . " World" yields "Hello World". The dot is not a plus (+); it does not add numbers, it joins strings.

To append to the same variable, the .= compound assignment is shorter. Instead of $msg = "Hi "; $msg .= "there"; you would otherwise write $msg = $msg . "there";. Both forms give the same result; .= is just shorter.

Common mistakes: . vs +

In PHP, . and + are different. "5" . "5" concatenates and gives "55"; "5" + "5" adds the numbers and gives 10. A number in quotes is a string; a number without quotes is a number.

The . converts both sides to strings and joins them. That is why "Age: " . 25 outputs "Age: 25". It turns the number into a string automatically. This is usually what you want; but typing . when you meant + can produce surprising results.

Exercise Grow a welcome message with .=

Assign "Welcome" to $msg. Then append ", Alex!" to $msg using .=. Finally print it with echo $msg;.

Show example solution 
First write $msg = "Welcome"; then append with $msg .= ", Alex!"; then echo $msg;
Example solution:
<?php
$msg = "Welcome";
$msg .= ", Alex!";
echo $msg;

Test yourself

  1. What is the output of echo "5" . "5";?

    echo "5" . "5";
    • 10
    • 5
    • 25
    • 55
    Show answer

    55 — Correct. The . joins strings; the two "5" strings become "55".

  2. Write the compound concatenation operator

    $msg = 'Hello';
$msg____ ' World';
echo $msg;
    Show answer 
    $msg = 'Hello';
$msg.= ' World';
echo $msg;

  3. Match each expression to its output

    '5' . '5'
    '55'
    5 + 5
    10
    'a' . 'b'
    'ab'

All lessons in Beginner

1 PHP basics

  1. What is PHP?
  2. PHP tags
  3. Output with echo
  4. Comments
  5. phpinfo() and PHP version
  6. Summary - PHP basics

2 Variables

  1. Declaring variables
  2. Variable naming rules
  3. Reassigning variables
  4. Combining variables
  5. Checking variables with isset() and unset()
  6. Summary - Variables

3 Data types

  1. string and int
  2. float and bool
  3. null and empty value
  4. Type checking with gettype()
  5. Detailed output with var_dump()
  6. Summary - Data types

4 Project: Calculator

  1. Project: Calculator
  2. Number input and operator selection
  3. Computing the operation
  4. Handling error cases
  5. Project final - Calculator

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Concatenation and increment
  6. Summary - Operators

6 String basics

  1. Creating strings
  2. Length with strlen()
  3. String concatenation
  4. Variable interpolation in double quotes
  5. Escape sequences
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. else and elseif
  3. The switch statement
  4. The ternary operator
  5. Comparison pitfalls
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. The foreach loop
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Project: Shopping cart
  2. Adding products to the cart
  3. Displaying the cart
  4. Computing the total
  5. Project final - Shopping cart

10 Array basics

  1. Creating arrays
  2. Accessing array elements
  3. Element count with count()
  4. Array output with print_r()
  5. Iterating an array
  6. Summary - Array basics

11 Array methods

  1. array_push() and array_pop()
  2. array_shift() and array_unshift()
  3. Merging with array_merge()
  4. Slicing with array_slice()
  5. in_array() and array_search()
  6. Summary - Array methods

12 Associative arrays

  1. Key-value pairs
  2. Accessing keys
  3. array_keys() and array_values()
  4. Key check with isset()
  5. Iterating associative arrays
  6. Summary - Associative arrays

13 Functions

  1. Defining functions
  2. Calling functions
  3. Returning values
  4. Function scope
  5. Returning arrays from functions
  6. Summary - Functions

14 Parameters

  1. Functions with parameters
  2. Default parameter values
  3. Multiple parameters
  4. Typed parameters
  5. Return type declaration
  6. Summary - Parameters

15 Project: To-do list

  1. Project: To-do list
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Project final - To-do list

16 Advanced string methods

  1. Replacing with str_replace()
  2. Slicing with substr()
  3. Searching with strpos()
  4. Splitting with explode()
  5. Joining with implode()
  6. Summary - Advanced string methods

17 Superglobals

  1. What is a superglobal?
  2. Receiving data with $_GET
  3. Receiving data with $_POST
  4. $_SERVER and server info
  5. Everything with $_REQUEST
  6. Summary - Superglobals

18 Forms

  1. Creating HTML forms
  2. Processing form data
  3. Security with htmlspecialchars()
  4. Form validation basics
  5. Showing error messages
  6. Summary - Forms

19 File inclusion

  1. Including files with include
  2. Including files with require
  3. include_once and require_once
  4. __DIR__ and path management
  5. Layout and partial logic
  6. Summary - File inclusion

20 Beginner final

  1. Challenge - Calculator
  2. Challenge - Secure feedback form
  3. Challenge - Array operations
  4. Challenge - Functions and loops
  5. Challenge - Mini CMS