Are there specific cases where using variables within strings in PHP can lead to unexpected results, and how can they be avoided?

Using variables within strings in PHP can lead to unexpected results when the string is enclosed in single quotes ('') instead of double quotes (""). To avoid this issue, always enclose strings that contain variables in double quotes to ensure that the variables are properly interpreted and replaced with their values.

$name = "Alice";
echo "Hello, $name!"; // Output: Hello, Alice!