A string is a data type used in programming to represent a sequence of characters. These characters can be letters, numbers, spaces, symbols, etc. In many programming languages, a string is enclosed in single quotes (') or double quotes (").

String Concatenation
Concatenation is the process of joining two or more strings together.

<?php
$name = "John";
$lastname = "Smith";

// Concatenate strings with the "." operator
$fullname = $name . " " . $lastname;
echo $fullname; // Output: John Smith
?>

Here, the . operator is used to concatenate the variables $name and $lastname, separated by a space.

Size of a String
To find out the number of characters in a string, we use the strlen() function.

<?php
$text = "Hello, World!";
$size = strlen($text);
echo $size; // Output: 13
?>

The strlen() function counts the number of characters, including spaces and punctuation.

Replacing Part of a String
The str_replace() function replaces all occurrences of a substring within a string.

<?php
$sentence = "I like apples";
$newSentence = str_replace("apples", "bananas", $sentence);
echo $newSentence;  // Output: I like bananas
?>

Here, the word "apples" was replaced with "bananas" in the original string.

Convert to Uppercase or Lowercase
You can use strtoupper() to convert a string to uppercase and strtolower() to convert it to lowercase.

<?php
$text = "Hello, World!";
$uppercase = strtoupper($text);
$lowercase = strtolower($text);

echo $uppercase;  // Output: HELLO, WORLD!
echo $lowercase;  // Output: hello, world!
?>

These functions are useful for standardizing the format of a string.

Get Part of a String
To extract part of a string, we use the substr() function.

<?php
$text = "Learning PHP is fun!";
$part = substr($text, 9, 3);
echo $part;  // Output: PHP
?>

Here, the substr() function starts at position 9 (index 0) and returns 3 characters from there.

Remove Whitespace from the Beginning and End
The trim() function removes whitespace (or other characters) from the beginning and end of a string.

<?php
$text = "    Hello, World!    ";
$clean = trim($text);
echo $clean;  // Output: "Hello, World!"
?>

This function is useful for cleaning strings received from forms or user input.

Break a String into an Array
The explode() function transforms a string into an array based on a delimiter.

<?php
$sentence = "PHP,JavaScript,Python";
$languages = explode(",", $sentence);

print_r($languages);
// Output: Array ( [0] => PHP [1] => JavaScript [2] => Python )
?>

Here, the explode() function splits the string into several parts, using the comma as the delimiter.

Join Elements of an Array into a String
The implode() function does the reverse of explode(), joining the elements of an array into a string.

<?php
$languages = array("PHP", "JavaScript", "Python");
$sentence = implode(" | ", $languages);

echo $sentence;  // Output: PHP | JavaScript | Python
?>

Find Position of Substring
The strpos() function returns the position of the first occurrence of a substring within a string.

<?php
$sentence = "I like to program in PHP";
$position = strpos($sentence, "PHP");

echo $position;  // Output: 23
?>

If the substring is not found, the function will return false.

Reverse a String
To reverse a string, you can use strrev().

<?php
$text = "Hello, World!";
$reversed = strrev($text);

echo $reversed;  // Output: !dlroW ,olleH
?>

You can run the code at https://onecompiler.com/php

Manipulating Strings with PHP