String replace functions in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to replace all occurrences of 'apple' with 'orange' in the string.

PHP

<?php
$text = "I like apple pie.";
$newText = str_replace([1], "orange", $text);
echo $newText;
?>

Drag options to blanks, or click blank then click option'

A"pear"

B"banana"

C"apple"

D"grape"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong string to replace.

Not putting the string to find in quotes.

The str_replace function replaces all occurrences of the first string with the second string. Here, we want to replace "apple" with "orange".

2fill in blank

medium

Complete the code to replace the first occurrence of 'cat' with 'dog' in the string.

PHP

<?php
$text = "The cat sat on the cat mat.";
$newText = preg_replace('/[1]/', "dog", $text, 1);
echo $newText;
?>

Drag options to blanks, or click blank then click option'

Adog

Bcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using the replacement string as the pattern.

Forgetting the slashes around the pattern.

The preg_replace function uses a pattern to find matches. Here, the pattern is '/cat/' to find the word 'cat'. The fourth argument '1' limits replacement to the first match.

3fill in blank

hard

Fix the error in the code to replace 'blue' with 'red' in the string.

PHP

<?php
$color = "blue";
$text = "The sky is blue.";
$newText = str_replace([1], "red", $text);
echo $newText;
?>

Drag options to blanks, or click blank then click option'

Ablue

Bcolor

C"color"

D$color

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the dollar sign for variables.

Passing the variable name as a string.

The variable $color holds the string 'blue'. To use it in str_replace, we must pass the variable name with the dollar sign.

4fill in blank

hard

Fill both blanks to create a dictionary of words and their replacements, then replace them in the text.

PHP

<?php
$text = "I have a cat and a dog.";
$replacements = array([1] => "dog", [2] => "cat");
$newText = str_replace(array_keys($replacements), array_values($replacements), $text);
echo $newText;
?>

Drag options to blanks, or click blank then click option'

A"cat"

B"dog"

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping keys and values.

Not using quotes around the words.

The array keys are the words to find, and the values are the words to replace them with. Here, "cat" is replaced with "dog" and "dog" is replaced with "cat".

5fill in blank

hard

Fill all three blanks to replace all vowels with '*' in the string using str_replace.

PHP

<?php
$text = "Hello World!";
$vowels = array([1]);
$stars = array([2]);
$newText = str_replace($vowels, $stars, [3]);
echo $newText;
?>

Drag options to blanks, or click blank then click option'

A"a", "e", "i", "o", "u"

B"*", "*", "*", "*", "*"

C$text

D"aeiou"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of an array for vowels or stars.

Forgetting the dollar sign for variables.

We create an array of vowels to find and an array of stars to replace them. Then we call str_replace with these arrays and the original text.

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