String search functions (strpos, strstr) in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the position of the word "world" in the string.

PHP

<?php
$text = "Hello world!";
$pos = [1]($text, "world");
echo $pos;
?>

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

Astrpos

Bstrstr

Csubstr

Dstrlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using strstr instead of strpos, which returns the substring instead of position.

Using substr which extracts part of the string.

Using strlen which returns string length.

The strpos function returns the position of the first occurrence of a substring in a string.

2fill in blank

medium

Complete the code to get the part of the string starting from "world".

PHP

<?php
$text = "Hello world!";
$part = [1]($text, "world");
echo $part;
?>

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

Astrstr

Bstr_replace

Cstrpos

Dsubstr

Attempts:

3 left

💡 Hint

Common Mistakes

Using strpos which returns position, not substring.

Using substr without position.

Using str_replace which replaces text.

The strstr function returns the part of the string starting from the first occurrence of the substring.

3fill in blank

hard

Fix the error in the code to correctly find the position of "test" in the string.

PHP

<?php
$text = "This is a test string.";
$pos = [1]($text, "test");
echo $pos;
?>

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

Astr_replace

Bstrpos

Csubstr

Dstrstr

Attempts:

3 left

💡 Hint

Common Mistakes

Using strstr instead of strpos.

Using substr which extracts substring by position.

Using str_replace which replaces text.

To find the position of a substring, use strpos. strstr returns the substring, not the position.

4fill in blank

hard

Fill both blanks to create a dictionary of words and their lengths for words longer than 3 characters.

PHP

<?php
$words = ["apple", "bat", "cat", "dog", "elephant"];
$lengths = array_filter(array_map(function($word) {
    return strlen($word);
}, $words));
$result = array_filter(array_combine($words, $lengths), function($length) {
    return $length [1] 3;
});
print_r($result);
?>

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

A==

B<

C>

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' which filters shorter words.

Using '==' which filters words exactly length 3.

Using '!=' which filters words not equal to length 3.

The code filters words with length greater than 3 using the '>' operator.

5fill in blank

hard

Fill all three blanks to create an array of words starting with 'a' and their lengths.

PHP

<?php
$words = ["apple", "banana", "apricot", "cherry", "avocado"];
$filtered = array_filter($words, function($word) {
    return [1]($word, 'a') === 0;
});
$lengths = array_map(function($word) {
    return [2]($word);
}, $filtered);
$result = array_combine($filtered, $lengths);
print_r($result);
?>

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

Astrpos

Bstrlen

Cstrstr

Dsubstr

Attempts:

3 left

💡 Hint

Common Mistakes

Using strstr which returns substring, not position.

Using substr which extracts substring by position.

Using wrong function for length.

The code uses strpos to check if the word starts with 'a' (position 0), and strlen to get word lengths.

Practice

1. What does the PHP function strpos do?

easy

A. Converts a string to uppercase

B. Extracts a substring starting from a specific character

C. Finds the position of a substring inside a string

D. Replaces a substring with another string

Solution

1. Step 1: Understand the purpose of strpos

   The strpos function searches for the first occurrence of a substring inside another string and returns its position.

2. Step 2: Compare with other options

   Options A, B, and C describe different string functions like strtoupper, strstr, and str_replace, which are not what strpos does.

3. Final Answer:

   Finds the position of a substring inside a string -> Option C

4. Quick Check:

   strpos = position finder [OK]

Hint: strpos returns position index of substring [OK]

Common Mistakes:

• Confusing strpos with strstr
• Thinking strpos extracts substring
• Assuming strpos replaces text

2. Which of the following is the correct syntax to find the position of 'cat' in the string $text = 'concatenate' using strpos?

easy

A. strpos('concatenate', 'cat')

B. strpos($text)

C. strpos('cat', $text)

D. strpos($text, 'cat')

Solution

1. Step 1: Identify correct parameter order for strpos

   The first parameter is the full string, the second is the substring to find. So strpos($text, 'cat') is correct.

2. Step 2: Check other options for errors

   strpos('concatenate', 'cat') uses a string literal instead of the variable. strpos('cat', $text) reverses parameters. strpos($text) misses the second parameter.

3. Final Answer:

   strpos($text, 'cat') -> Option D

4. Quick Check:

   strpos(string, substring) [OK]

Hint: First argument is full string, second is substring [OK]

Common Mistakes:

• Swapping the order of parameters
• Omitting the substring argument
• Passing substring as first argument

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

$text = 'hello world';
$pos = strpos($text, 'world');
echo $pos;

medium

A. 6

B. 5

C. 0

D. false

Solution

1. Step 1: Find the position of 'world' in 'hello world'

   The string 'hello world' has 'world' starting at index 6 (counting from 0).

2. Step 2: Understand what strpos returns

   strpos returns the starting position of the substring, so it returns 6.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   Position of 'world' in 'hello world' = 6 [OK]

Hint: Count characters from zero to substring start [OK]

Common Mistakes:

• Counting from 1 instead of 0
• Confusing position with length
• Expecting boolean true instead of position

4. The following code is intended to check if the word 'apple' exists in $fruit. What is the error?

$fruit = 'pineapple';
if (strpos($fruit, 'apple')) {
  echo 'Found';
} else {
  echo 'Not found';
}

medium

A. strpos returns false if found, so condition is wrong

B. strpos returns 0 for 'apple' position, which is treated as false

C. Missing third parameter in strpos

D. Syntax error in if statement

Solution

1. Step 1: Understand strpos return values

   strpos returns 0 if the substring is found at the start (index 0). In PHP, 0 is treated as false in conditions.

2. Step 2: Analyze the if condition behavior

   The condition if (strpos(...)) fails when strpos returns 0, so it wrongly goes to else.

3. Final Answer:

   strpos returns 0 for 'apple' position, which is treated as false -> Option B

4. Quick Check:

   Check strpos !== false to avoid 0 as false [OK]

Hint: Check strpos !== false, not just if() [OK]

Common Mistakes:

• Using if(strpos()) without strict false check
• Assuming strpos returns boolean true/false only
• Ignoring 0 as valid position

5. Given the string $sentence = 'The quick brown fox jumps', which code snippet correctly extracts the substring starting from the word 'brown' using strstr?

hard

A. echo strstr($sentence, 'brown');

B. echo strstr($sentence, 'brown', true);

C. echo strpos($sentence, 'brown');

D. echo substr($sentence, strpos($sentence, 'brown'));

Solution

1. Step 1: Understand strstr behavior

   strstr returns the part of the string starting from the first occurrence of the substring, including it.

2. Step 2: Analyze options

   echo strstr($sentence, 'brown'); correctly uses strstr to get substring from 'brown'. echo strstr($sentence, 'brown', true); returns part before 'brown'. echo strpos($sentence, 'brown'); returns position, not substring. echo substr($sentence, strpos($sentence, 'brown')); uses substr with strpos, which also works but is not strstr.

3. Final Answer:

   echo strstr($sentence, 'brown'); -> Option A

4. Quick Check:

   strstr returns substring from needle [OK]

Hint: strstr returns substring from needle, true returns before [OK]

Common Mistakes:

• Using third parameter true to get substring after needle
• Confusing strpos with strstr
• Expecting strpos to return substring