String replace functions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of str_replace with overlapping replacements

What is the output of the following PHP code?

PHP

<?php
$text = "abcabc";
$result = str_replace("abc", "x", $text);
echo $result;
?>

A xx

B abcabc

C xabc

D xxabc

💡 Hint

str_replace replaces all occurrences of the search string.

The function replaces every 'abc' with 'x'. Since 'abc' appears twice, the output is 'xx'.

❓ Predict Output

intermediate

Behavior of str_ireplace with case insensitive replacement

What will be the output of this PHP code?

PHP

<?php
$text = "Hello World!";
$result = str_ireplace("hello", "Hi", $text);
echo $result;
?>

A Hi hello World!

B hello World!

C Hello World!

D Hi World!

💡 Hint

str_ireplace ignores case when searching.

str_ireplace replaces 'hello' ignoring case, so 'Hello' becomes 'Hi'.

❓ Predict Output

advanced

Output of str_replace with array replacements

What is the output of this PHP code snippet?

PHP

<?php
$text = "I like cats and dogs.";
$result = str_replace(["cats", "dogs"], ["birds", "fish"], $text);
echo $result;
?>

A I like birds and dogs.

B I like birds and fish.

C I like cats and dogs.

D I like fish and birds.

💡 Hint

When arrays are used, replacements happen pairwise.

Each element in the search array is replaced by the corresponding element in the replacement array.

❓ Predict Output

advanced

Result of str_replace when search string is empty

What will this PHP code output?

PHP

<?php
$text = "hello";
$result = str_replace("", "x", $text);
echo $result;
?>

A xhelxloxlo

B hello

C xhello

D SyntaxError

💡 Hint

Replacing an empty string inserts the replacement between every character and at the start and end.

Replacing empty string inserts 'x' before, between, and after characters, resulting in 'xhelxloxlo'.

❓ Predict Output

expert

Output of nested str_replace calls

What is the output of this PHP code?

PHP

<?php
$text = "abc";
$result = str_replace("a", "b", str_replace("b", "c", $text));
echo $result;
?>

A acc

B ccc

C bcc

D bbc

💡 Hint

Inner str_replace runs first, then outer one.

Inner replaces 'b' with 'c' → 'acc'. Outer replaces 'a' with 'b' → 'bcc'.