在PHP中，使用點（.）運算符連接字符串。例如，echo "Hello" . "World"; 輸出 HelloWorld；可以將字符串存儲在變量中再連接，如 $greeting = "Hello"; $name = "John"; echo $greeting . $name; 輸出 HelloJohn；若需空格或標點，必須手動添加；也可將變量與文本混合使用，如 $message = "Welcome, " . $name . "! Thank you for logging in.";；建議注意引號使用、合理加空格及標點；可在循環(huán)中逐步構建字符串，如使用 $output .= "- " . $item . "
";；常見錯誤包括誤用加號（ ）和引號嵌套未正確處理，如 echo 'Hello $name'; 不會解析變量，應改為 echo 'Hello ' . $name;。

In PHP, you concatenate strings using the dot (.) operator. It’s a straightforward way to combine two or more strings into one.

Basic Usage of the . Operator

The main thing to know is that in PHP, the sign doesn’t work for combining text — you have to use the . instead.
For example:

echo "Hello" . "World"; // Outputs: HelloWorld

You can also store parts of the string in variables and then join them:

$greeting = "Hello";
$name = "John";
echo $greeting . $name; // Outputs: HelloJohn

One thing to watch out for: if you don't add spaces or punctuation manually, PHP won't do it for you. So if you want a space between words, you need to include it in one of the strings or add it as a separate part.

Combining Strings with Variables and Text

A common situation is when you're building a sentence that includes both static text and dynamic values (like user input or database results). You can mix variables and literal strings freely.

Here's how you might build a message:

$name = "Sarah";
$message = "Welcome, " . $name . "! Thank you for logging in.";
echo $message;
// Outputs: Welcome, Sarah! Thank you for logging in.

This approach works well in many scenarios like generating HTML content dynamically or preparing messages to display on a webpage.

Some tips:

• Keep an eye on quotation marks — especially when mixing single and double quotes.
• Use parentheses if needed to make complex concatenation easier to read.
• Don’t forget to include spaces or punctuation where necessary.

Concatenating in Larger Blocks or Loops

Sometimes you’ll want to build up a string gradually — for instance, looping through an array and collecting output line by line.

Here’s a basic loop example:

$items = ["apple", "banana", "cherry"];
$output = "";
foreach ($items as $item) {
    $output .= "- " . $item . "<br>";
}
echo $output;

In this case, we start with an empty string and keep adding to it using .= (which is short for $output = $output . "something").

This method is often used for:

• Building lists or tables dynamically
• Preparing email content from multiple sources
• Creating custom log entries

Make sure you initialize your variable before the loop starts, or you’ll get errors.

A Couple Common Mistakes to Avoid

It’s easy to make small mistakes that break your code. Here are two common ones:

• Using instead of .: PHP will try to convert your strings to numbers and add them, which leads to unexpected results or even silent errors.
• Mixing quotes without escaping properly: If you’re inside single quotes and try to use a variable, it won’t be interpreted correctly unless you close the quote or use double quotes.

Example of something that won't work:

echo 'Hello $name'; // Outputs: Hello $name, not Hello Sarah

Instead, either use double quotes or concatenate the variable:

echo 'Hello ' . $name;

基本上就這些。

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