String search functions (strpos, strstr) in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of strpos with needle at start?

Consider the following PHP code snippet. What will be the output when searching for the substring 'Hello' in the string 'Hello World' using strpos?

PHP

<?php
$pos = strpos('Hello World', 'Hello');
echo $pos;
?>

A false

B 1

C null

D 0

💡 Hint

Remember that strpos returns the position index starting at 0.

The substring 'Hello' starts at the very beginning of the string, so strpos returns 0, which is a valid position.

❓ Predict Output

intermediate

What does strstr return when substring is found?

What will be the output of this PHP code using strstr to find 'World' in 'Hello World'?

PHP

<?php
$result = strstr('Hello World', 'World');
echo $result;
?>

A World

B Hello World

C orld

D false

💡 Hint

strstr returns the part of the string starting from the first occurrence of the needle.

strstr returns the substring starting from 'World' to the end, which is 'World'.

❓ Predict Output

advanced

What is the output when strpos needle is not found?

What will this PHP code output when searching for 'abc' in 'defgh' using strpos?

PHP

<?php
$pos = strpos('defgh', 'abc');
var_dump($pos);
?>

A 0

B bool(false)

C int(0)

D null

💡 Hint

If the substring is not found, strpos returns false.

Since 'abc' is not in 'defgh', strpos returns boolean false, and var_dump shows bool(false).

❓ Predict Output

advanced

What does strstr return with before_needle=true?

What will this PHP code output when using strstr with the third parameter true to find 'World' in 'Hello World'?

PHP

<?php
$result = strstr('Hello World', 'World', true);
echo $result;
?>

A Hello

B Hello World

C World

D false

💡 Hint

When before_needle is true, strstr returns the part before the needle.

With before_needle=true, strstr returns the substring before 'World', which is 'Hello '.

🧠 Conceptual

expert

Why strpos can return 0 but still be true in condition?

In PHP, why does this code print 'Not Found' even though strpos returns 0?

A Because 0 is treated as false, so it prints 'Found' anyway

B Because the condition treats 0 as false, so it prints 'Not Found', but the code prints 'Found' due to a bug

C Because strpos returns false on failure, and 0 is treated as false, so it prints 'Not Found'

D Because 0 is treated as false, so it prints 'Not Found'

💡 Hint

Check how PHP treats 0 and false in if conditions.

strpos returns 0 when the substring is at the start, but 0 is false in PHP conditions, so the if condition fails and prints 'Not Found'. The code prints 'Found' only if strpos returns a non-false, non-zero value.