What are the possible reasons for receiving unexpected results when manipulating strings in PHP?

When manipulating strings in PHP, unexpected results can occur due to issues such as incorrect use of string functions, encoding mismatches, or unexpected whitespace characters. To solve this, ensure that you are using the correct string functions for the desired operation, pay attention to character encoding, and trim or sanitize input strings to remove any unwanted whitespace.

// Example: Removing whitespace before comparing strings
$string1 = "hello";
$string2 = "hello ";

// Remove whitespace using trim() before comparing
if (trim($string1) === trim($string2)) {
    echo "Strings are equal after removing whitespace.";
} else {
    echo "Strings are not equal.";
}