String replace functions in PHP - Mini Project: Build & Apply

String replace functions

📖 Scenario: You are working on a simple text editor feature that needs to replace certain words in a sentence.

🎯 Goal: Build a PHP script that replaces specific words in a given sentence using string replace functions.

📋 What You'll Learn

Create a string variable with a given sentence

Create a variable with the word to find

Use a string replace function to replace the word

Print the updated sentence

💡 Why This Matters

🌍 Real World

Replacing words in text is common in text editors, chat applications, and content management systems.

💼 Career

Understanding string replacement helps in data cleaning, user input processing, and building dynamic text features.

1

Create the initial sentence

Create a string variable called sentence and set it to the exact value: 'I love programming in PHP.'

PHP

# Create a string variable called sentence with the value 'I love programming in PHP.'
# Your code here

Hint

Use $sentence = 'your text'; to create the string variable.

2

Set the word to replace

Create a string variable called wordToReplace and set it to the exact value: 'PHP'

PHP

<?php
$sentence = 'I love programming in PHP.';
# Create a string variable called wordToReplace with the value 'PHP'
# Your code here

Hint

Use $wordToReplace = 'PHP'; to create the variable.

3

Replace the word in the sentence

Use the PHP function str_replace to replace $wordToReplace with 'JavaScript' in $sentence. Store the result back in $sentence.

PHP

<?php
$sentence = 'I love programming in PHP.';
$wordToReplace = 'PHP';
# Replace $wordToReplace with 'JavaScript' in $sentence and save it back to $sentence
# Your code here

Hint

Use str_replace($wordToReplace, 'JavaScript', $sentence) to replace the word.

4

Print the updated sentence

Write a print statement to display the updated $sentence.

PHP

<?php
$sentence = 'I love programming in PHP.';
$wordToReplace = 'PHP';
$sentence = str_replace($wordToReplace, 'JavaScript', $sentence);
# Print the updated sentence
# Your code here

Hint

Use print($sentence); to show the result.

Practice

1. Which PHP function is used to replace all occurrences of a string with another string?

easy

A. strpos()

B. str_replace()

C. substr()

D. strlen()

Solution

1. Step 1: Understand the purpose of str_replace()

   The function str_replace() replaces all occurrences of a search string with a replacement string in a given text.

2. Step 2: Compare with other functions

   substr() extracts part of a string, strpos() finds position of a substring, strlen() returns string length. None replace text.

3. Final Answer:

   str_replace() -> Option B

4. Quick Check:

   Replace text = str_replace() [OK]

Hint: Remember: str_replace replaces text, others do different tasks [OK]

Common Mistakes:

• Confusing str_replace with substr
• Using strpos instead of replace
• Expecting strlen to replace text

2. Which of the following is the correct syntax to replace 'cat' with 'dog' in the string $text using PHP?

easy

A. str_replace('dog', 'cat', $text);

B. replace('cat', 'dog', $text);

C. str_replace($text, 'cat', 'dog');

D. str_replace('cat', 'dog', $text);

Solution

1. Step 1: Check the correct parameter order of str_replace()

   The correct order is str_replace(search, replace, subject). So 'cat' is search, 'dog' is replace, $text is subject.

2. Step 2: Validate each option

   str_replace('cat', 'dog', $text); matches correct order. replace('cat', 'dog', $text); uses a non-existent function. str_replace($text, 'cat', 'dog'); swaps parameters incorrectly. str_replace('dog', 'cat', $text); swaps search and replace.

3. Final Answer:

   str_replace('cat', 'dog', $text); -> Option D

4. Quick Check:

   str_replace(search, replace, subject) [OK]

Hint: Remember parameter order: search, replace, then subject [OK]

Common Mistakes:

• Swapping search and replace
• Using wrong function name
• Incorrect parameter order

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

$text = "I love apples.";
$result = str_replace("apples", "oranges", $text);
echo $result;

medium

A. I love oranges.

B. I love apples.

C. I love apples.oranges

D. Syntax error

Solution

1. Step 1: Understand str_replace behavior

   str_replace replaces all occurrences of the search string with the replacement string in the given text.

2. Step 2: Apply replacement to the string

   "apples" is replaced by "oranges" in "I love apples.", resulting in "I love oranges.".

3. Final Answer:

   I love oranges. -> Option A

4. Quick Check:

   Replace 'apples' with 'oranges' = I love oranges. [OK]

Hint: str_replace returns new string; echo the result to see changes [OK]

Common Mistakes:

• Expecting original string unchanged
• Not assigning result to variable
• Syntax errors in code

4. Identify the error in the following PHP code snippet:

$text = "Hello world!";
str_replace('world', 'PHP', $text);
echo $text;

medium

A. Missing third argument in str_replace

B. Syntax error in str_replace call

C. str_replace does not modify $text directly

D. echo statement is incorrect

Solution

1. Step 1: Check str_replace usage

   The str_replace call has the correct three arguments: search='world', replace='PHP', subject=$text.

2. Step 2: Understand string immutability in PHP

   str_replace returns a new string; it does not change the original string $text unless assigned back, e.g., $text = str_replace('world', 'PHP', $text);

3. Final Answer:

   str_replace does not modify $text directly -> Option C

4. Quick Check:

   Assign result to variable to update string [OK]

Hint: Assign str_replace result to variable; original string stays same [OK]

Common Mistakes:

• Not assigning result back to variable
• Assuming str_replace changes string in place

5. You want to replace multiple words in a string at once: replace 'red' with 'blue' and 'green' with 'yellow' in $text. Which code correctly does this in PHP?

hard

A. $result = str_replace(['red', 'green'], ['blue', 'yellow'], $text);

B. $result = str_replace('red', 'blue', $text);
str_replace('green', 'yellow', $text);

C. $result = str_replace('red', 'blue', $text) && str_replace('green', 'yellow', $text);

D. $result = str_replace('red' => 'blue', 'green' => 'yellow', $text);

Solution

1. Step 1: Understand str_replace with arrays

   str_replace accepts arrays for search and replace to perform multiple replacements in one call.

2. Step 2: Analyze each option

   $result = str_replace(['red', 'green'], ['blue', 'yellow'], $text); uses arrays correctly. $result = str_replace('red', 'blue', $text); str_replace('green', 'yellow', $text); performs first replacement but second call discards result and uses original $text, so 'green' remains. $result = str_replace('red', 'blue', $text) && str_replace('green', 'yellow', $text); uses && which returns boolean, not string. $result = str_replace('red' => 'blue', 'green' => 'yellow', $text); uses invalid syntax.

3. Final Answer:

   $result = str_replace(['red', 'green'], ['blue', 'yellow'], $text); -> Option A

4. Quick Check:

   Use arrays in str_replace for multiple replacements [OK]

Hint: Use arrays in str_replace to replace many words at once [OK]

Common Mistakes:

• Using multiple str_replace without chaining
• Using logical operators instead of chaining
• Wrong syntax for arrays in str_replace