Lecture Notes: Class 10
Strings and String Functions in PHP
Objective:
1.
Learn to manipulate strings and use string
functions in PHP.
2.
Practice common string operations like
concatenation and replacement.
Outcome:
By the end of this class,
students will be able to:
- Understand
and use common string functions such as strlen(), strpos(), substr(), and
str_replace().
- Perform
string operations like concatenation, search, and replacement.
1. Introduction to
Strings in PHP
A string is a sequence of
characters. In PHP, strings are used to store text data and can include
letters, numbers, and symbols. Strings are commonly used to process user input,
manipulate text, and generate dynamic content in PHP applications.
Creating Strings
Strings in PHP can be
created using:
- Single
quotes (' '): Useful when you don’t need to
include variables inside the string.
- Double
quotes (" "): Allows variable interpolation
(inserting variable values directly in the string).
- Examples:
$name = 'Alice'; // Using single quotes
$greeting = "Hello,
$name!"; // Using double quotes
with variable interpolation
2. Common String
Functions in PHP
PHP provides several
built-in functions to manipulate strings effectively. Below are some essential
string functions:
a. strlen() - String
Length
The strlen() function
returns the length of a string (i.e., the number of characters, including
spaces).
Syntax:
strlen(string $string):
int
Example:
$text = "Hello,
PHP!";
$length = strlen($text);
echo "The length of
the text is: " . $length; // Output: 11
b. strpos() - Find
Position of a Substring
The strpos() function
finds the position of the first occurrence of a substring in a string. If the
substring is not found, it returns false.
Syntax:
strpos(string $haystack,
string $needle, int $offset = 0): int|false
Example:
$phrase = "Learning
PHP is fun!";
$position =
strpos($phrase, "PHP");
if ($position !== false)
{
echo "The word 'PHP' starts at
position: " . $position; // Output: 9
}
c. substr() - Extract a
Substring
The substr() function
extracts a portion of a string based on a starting index and an optional
length.
Syntax:
substr(string $string,
int $start, int $length = null): string
Example:
$text = "Hello,
World!";
$substring =
substr($text, 7, 5);
echo $substring; //
Output: World
d. str_replace() -
Replace Substring
The str_replace()
function replaces occurrences of a substring within a string with another
substring.
Syntax:
str_replace(mixed
$search, mixed $replace, mixed $subject, int &$count = null): mixed
Example:
$text = "I love
JavaScript!";
$replaced_text =
str_replace("JavaScript", "PHP", $text);
echo $replaced_text; //
Output: I love PHP!
3. String Concatenation
in PHP
Concatenation is the
process of joining two or more strings together. In PHP, concatenation is done
using the dot (.) operator.
Example:
$firstName =
"John";
$lastName =
"Doe";
$fullName = $firstName .
" " . $lastName;
echo $fullName; //
Output: John Doe
4. Additional Useful
String Functions
a. strtolower() and
strtoupper()
- strtolower()
converts a string to lowercase.
- strtoupper()
converts a string to uppercase.
Example:
$text = "Hello
World!";
echo strtolower($text);
// Output: hello world!
echo strtoupper($text);
// Output: HELLO WORLD!
b. ucfirst() and
ucwords()
- ucfirst()
capitalizes the first letter of a string.
- ucwords()
capitalizes the first letter of each word in a string.
Example:
$text = "hello
world!";
echo ucfirst($text); //
Output: Hello world!
echo ucwords($text); //
Output: Hello World!
5. Practical Examples and
Exercises
Exercise 1: Check if a
Word Exists in a Sentence
Write a PHP script to
check if the word "PHP" exists in the sentence "I am learning
PHP programming." If it does, output the position of the word.
$sentence = "I am
learning PHP programming.";
$word = "PHP";
$position =
strpos($sentence, $word);
if ($position !== false)
{
echo "The word 'PHP' was found at
position: " . $position;
} else {
echo "The word 'PHP' was not
found.";
}
Exercise 2: Extract and
Modify a Substring
Given the string
"Learning PHP is easy and fun!", use substr() to extract the word
"easy" and replace it with "exciting" using str_replace().
$text = "Learning
PHP is easy and fun!";
$substring =
substr($text, 15, 4); // Extracts "easy"
$new_text =
str_replace("easy", "exciting", $text);
echo $new_text; //
Output: Learning PHP is exciting and fun!
Summary
In this class, we
covered:
- Basic
string functions (strlen(), strpos(), substr(), and
str_replace()) for manipulating strings.
- String
concatenation to join strings using the .
operator.
- Additional
functions for changing the case of strings,
like strtolower(), strtoupper(), ucfirst(), and ucwords().
Next Steps
In the next class, we’ll
dive deeper into handling user inputs and sanitizing strings for web
applications. Practicing these string functions will build a strong foundation
for text processing tasks commonly required in PHP applications.
Assignment
1.
Write a PHP script that accepts a string
and returns it in uppercase, lowercase, and with the first letter of each word
capitalized.
2.
Create a script that finds the length of a
string, finds a particular word within it, and replaces that word with another
word provided by the user.