Substring extraction in PHP - Mini Project: Build & Apply

Substring extraction

📖 Scenario: Imagine you have a list of book titles, and you want to extract a short preview from each title to show on a website.

🎯 Goal: You will create a PHP program that extracts a substring (a part of a string) from each book title to create a preview snippet.

📋 What You'll Learn

Create an array of book titles

Set a variable for the length of the preview substring

Use a loop to extract the substring from each title

Print the preview snippets

💡 Why This Matters

🌍 Real World

Extracting substrings is useful for showing previews or summaries of longer text, like book titles, article headlines, or product names on websites.

💼 Career

Many programming jobs require manipulating text data, and substring extraction is a common task in web development, data processing, and user interface design.

1

Create an array of book titles

Create an array called books with these exact titles: 'The Great Gatsby', 'To Kill a Mockingbird', '1984', 'Pride and Prejudice', 'Moby-Dick'.

PHP

# Create the array 'books' with the given titles
# Your code here

Hint

Use square brackets [] to create the array and separate each title with commas.

2

Set the preview length

Create a variable called previewLength and set it to 10 to define how many characters to extract from each title.

PHP

<?php
$books = ['The Great Gatsby', 'To Kill a Mockingbird', '1984', 'Pride and Prejudice', 'Moby-Dick'];
# Set 'previewLength' to 10
# Your code here

Hint

Use the = sign to assign the number 10 to the variable previewLength.

3

Extract substrings from each title

Use a foreach loop with variable $title to go through $books. Inside the loop, create a variable $preview that uses substr($title, 0, $previewLength) to get the first 10 characters of each title.

PHP

<?php
$books = ['The Great Gatsby', 'To Kill a Mockingbird', '1984', 'Pride and Prejudice', 'Moby-Dick'];
$previewLength = 10;
# Use foreach loop to extract substring previews
# Your code here

Hint

Use foreach ($books as $title) to loop, and substr() to get the substring.

4

Print the preview snippets

Inside the foreach loop, add a print statement to display $preview followed by a newline using "\n".

PHP

<?php
$books = ['The Great Gatsby', 'To Kill a Mockingbird', '1984', 'Pride and Prejudice', 'Moby-Dick'];
$previewLength = 10;
foreach ($books as $title) {
    $preview = substr($title, 0, $previewLength);
    # Print the preview with a newline
    # Your code here
}

Hint

Use print($preview . "\n") to show each preview on its own line.

Practice

1. What does the PHP function substr($text, 2, 3) do?

easy

A. Extracts the first 3 characters of $text

B. Extracts 2 characters from $text starting at index 3

C. Extracts 3 characters from $text starting at index 2

D. Extracts the last 3 characters of $text

Solution

1. Step 1: Understand substr parameters

   The first parameter is the string, the second is the start index (0-based), and the third is the length of substring.

2. Step 2: Apply to given function

   Starting at index 2 means the third character, and length 3 means extract 3 characters from there.

3. Final Answer:

   Extracts 3 characters from $text starting at index 2 -> Option C

4. Quick Check:

   substr(string, 2, 3) = 3 chars from index 2 [OK]

Hint: Remember start is zero-based, length is how many chars [OK]

Common Mistakes:

• Confusing start index with length
• Thinking start counts from 1 instead of 0
• Assuming length is mandatory

2. Which of the following is the correct syntax to extract a substring from a string $str starting at position 4 with length 5 in PHP?

easy

A. substr($str, 5);

B. substr($str, 4, 5);

C. substr($str, 4);

D. substr($str, 5, 4);

Solution

1. Step 1: Recall substr syntax

   substr(string, start, length) extracts substring starting at 'start' index with 'length' characters.

2. Step 2: Match parameters to question

   Start is 4, length is 5, so substr($str, 4, 5) is correct syntax.

3. Final Answer:

   substr($str, 4, 5); -> Option B

4. Quick Check:

   substr($str, 4, 5) = correct syntax [OK]

Hint: Syntax is substr(string, start, length) with start zero-based [OK]

Common Mistakes:

• Swapping start and length values
• Omitting length when needed
• Using 1-based start index

3. What will be the output of the following PHP code?

$text = "Hello World!";
echo substr($text, 6, 5);

medium

A. World

B. World!

C. Hello

D. orld!

Solution

1. Step 1: Identify substring start and length

   Start index is 6 (0-based), length is 5 characters.

2. Step 2: Extract substring from "Hello World!"

   Index 6 is 'W', next 5 chars are 'World'.

3. Final Answer:

   World -> Option A

4. Quick Check:

   substr("Hello World!", 6, 5) = "World" [OK]

Hint: Count characters from zero, then take length chars [OK]

Common Mistakes:

• Including the exclamation mark mistakenly
• Starting count from 1 instead of 0
• Confusing length with end index

4. The following PHP code is intended to extract the substring "cat" from the string "concatenate". What is wrong?

$word = "concatenate";
echo substr($word, 3, 4);

medium

A. The length parameter is too long; it should be 3

B. The start index should be 4 instead of 3

C. The substr function cannot extract "cat" from this string

D. There is no error; the code works correctly

Solution

1. Step 1: Locate substring "cat" in "concatenate"

   "cat" starts at index 3: c(3), a(4), t(5).

2. Step 2: Check length parameter

   Length 4 extracts "cate" (4 chars), but "cat" is only 3 chars, so length should be 3.

3. Final Answer:

   The length parameter is too long; it should be 3 -> Option A

4. Quick Check:

   substr("concatenate", 3, 3) = "cat" [OK]

Hint: Count exact substring length to avoid extra chars [OK]

Common Mistakes:

• Using wrong start index
• Assuming substr auto-trims extra chars
• Thinking substr can't extract middle parts

5. You have a string $data = "user:john;id:12345;role:admin";. How do you extract the user name "john" using substr and strpos functions in PHP?

hard

A. substr($data, 0, strpos($data, ':'));

B. substr($data, 5, 4);

C. substr($data, strpos($data, ';') + 1, 4);

D. substr($data, strpos($data, ':') + 1, strpos($data, ';') - strpos($data, ':') - 1);

Solution

1. Step 1: Find start position of username

   Use strpos($data, ':') to find colon after "user", add 1 to start after colon.

2. Step 2: Find length of username substring

   Find position of first semicolon with strpos($data, ';'), subtract start position and 1 to get length.

3. Step 3: Use substr with calculated start and length

   substr($data, start, length) extracts "john" correctly.

4. Final Answer:

   substr($data, strpos($data, ':') + 1, strpos($data, ';') - strpos($data, ':') - 1); -> Option D

5. Quick Check:

   Use strpos to find delimiters, substr extracts between them [OK]

Hint: Use strpos to find delimiters, substr extracts between them [OK]

Common Mistakes:

• Hardcoding start and length without dynamic positions
• Using wrong delimiter positions
• Extracting wrong substring part