String replace functions in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the PHP function str_replace() do?

It replaces all occurrences of a search string with a replacement string within another string.

beginner

How do you replace the word 'cat' with 'dog' in the string 'The cat is cute' using PHP?

Use str_replace('cat', 'dog', 'The cat is cute') which returns 'The dog is cute'.

intermediate

What is the difference between str_replace() and str_ireplace() in PHP?

str_replace() is case-sensitive, while str_ireplace() ignores case when replacing strings.

intermediate

Can str_replace() replace multiple different strings at once?

Yes, by passing arrays for the search and replace parameters, it can replace multiple strings in one call.

intermediate

What does the optional fourth parameter of str_replace() do?

It stores the number of replacements made as an integer.

Which PHP function replaces all occurrences of a string, ignoring case?

A str_ireplace()

B str_replace()

C substr_replace()

D strtolower()

str_ireplace() replaces strings without considering case differences.

What will str_replace('a', 'b', 'apple') return?

A bpple

B apple

C bppleapple

D bppleappleb

All 'a' characters are replaced with 'b', so 'apple' becomes 'bpple'.

How can you replace multiple different words in one call using str_replace()?

A By using regular expressions

B By calling <code>str_replace()</code> multiple times

C By passing arrays for search and replace parameters

D By using <code>str_ireplace()</code>

Passing arrays lets you replace multiple strings in one function call.

What does the optional fourth parameter of str_replace() store?

A The replaced string

B Length of the original string

C Boolean success/failure

D Number of replacements made

It stores the count of how many replacements were done.

Which function would you use to replace a substring at a specific position in PHP?

A str_replace()

B substr_replace()

C str_ireplace()

D strpos()

substr_replace() replaces part of a string at a given position.

Explain how to replace multiple different words in a string using PHP string replace functions.

Think about how arrays can be used as inputs.

Describe the difference between str_replace() and str_ireplace().

Focus on how they treat uppercase and lowercase letters.

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