String concatenation

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

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".

Write the compound concatenation operator

$msg = 'Hello';
$msg____ ' World';
echo $msg;

Show answer

$msg = 'Hello';
$msg.= ' World';
echo $msg;

Match each expression to its output

'5' . '5'

'55'
5 + 5

10
'a' . 'b'

'ab'

Next lesson: Variable interpolation in double quotes

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