A string in PHP is a sequence of characters (text).

$name = "Aditya";
echo $name;

🔹 1. String Functions (Important Built-in Functions)

PHP provides many built-in functions to work with strings.

📌 Common String Functions

$str = "Hello World";// Length of string
echo strlen($str); // 11// Convert to lowercase
echo strtolower($str); // hello world// Convert to uppercase
echo strtoupper($str); // HELLO WORLD// First letter capital
echo ucfirst("hello"); // Hello// First letter of each word
echo ucwords("hello world"); // Hello World// Reverse string
echo strrev("Hello"); // olleH// Find position
echo strpos($str, "World"); // 6// Replace text
echo str_replace("World", "PHP", $str); // Hello PHP

🔹 2. String Manipulation

String manipulation means modifying or working with strings.

📌 Concatenation (Joining Strings)

$first = "Hello";
$second = "World";echo $first . " " . $second; // Hello World

📌 Substring

echo substr("Hello World", 0, 5); // Hello

📌 Trim (Remove Spaces)

$str = "  Hello  ";
echo trim($str); // "Hello"

📌 Compare Strings

if ("apple" == "apple") {
    echo "Same";
}

🔹 3. Explode / Implode

These are very important for working with arrays and strings.

📌 explode() → String ➝ Array

Splits a string into an array.

$str = "apple,banana,mango";
$arr = explode(",", $str);print_r($arr);

👉 Output:

Array ( [0] => apple [1] => banana [2] => mango )

📌 implode() → Array ➝ String

Joins array elements into a string.

$arr = ["apple", "banana", "mango"];
$str = implode(",", $arr);echo $str; // apple,banana,mango

🔹 4. Regular Expressions (Regex)

Regex is used to match, search, or replace patterns in strings.

PHP uses functions like:

preg_match()
preg_replace()
preg_match_all()

📌 preg_match() (Check Pattern)

$str = "Hello123";if (preg_match("/[0-9]/", $str)) {
    echo "Number found";
}

📌 preg_replace() (Replace Pattern)

$str = "Hello123";echo preg_replace("/[0-9]/", "", $str);
// Output: Hello

📌 preg_match_all() (Find All Matches)

$str = "abc123xyz456";preg_match_all("/[0-9]+/", $str, $matches);print_r($matches);

📌 Common Regex Patterns

Pattern	Meaning
`/[0-9]/`	Any number
`/[a-z]/`	Lowercase letters
`/[A-Z]/`	Uppercase letters
`/^[a-z]+$/`	Only lowercase letters
`/^\d+$/`	Only numbers
`/^[a-zA-Z0-9]+$/`	Alphanumeric

🎯 Real Example (Form Validation)

$email = "test@gmail.com";if (preg_match("/^[\w\.-]+@[\w\.-]+\.\w+$/", $email)) {
    echo "Valid Email";
} else {
    echo "Invalid Email";
}

🚀 Summary

String Functions → Ready-made tools (strlen, strtoupper, etc.)
String Manipulation → Modify strings (concat, substr, trim)
explode() / implode() → Convert between string ↔ array
Regex → Advanced pattern matching & validation

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7. Strings (PHP)