String comparison functions in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to compare two strings for equality.

PHP

<?php
$string1 = "apple";
$string2 = "apple";
if ($string1 [1] $string2) {
    echo "Strings are equal.";
} else {
    echo "Strings are not equal.";
}
?>

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

A==

B===

C!=

D<>

Attempts:

3 left

💡 Hint

Common Mistakes

Using != which checks for inequality.

Using === which also checks type, not just value.

The operator == checks if two strings have the same value.

2fill in blank

medium

Complete the code to compare two strings ignoring case.

PHP

<?php
$string1 = "Hello";
$string2 = "hello";
if ([1]($string1, $string2) === 0) {
    echo "Strings are equal ignoring case.";
} else {
    echo "Strings are different.";
}
?>

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

Astrcmp

Bstrcasecmp

Cstrnatcmp

Dstrncmp

Attempts:

3 left

💡 Hint

Common Mistakes

Using strcmp which is case-sensitive.

Using strncmp which compares only part of the strings.

The function strcasecmp compares two strings ignoring case differences.

3fill in blank

hard

Fix the error in the code to correctly compare the first 3 characters of two strings.

PHP

<?php
$string1 = "abcdef";
$string2 = "abcxyz";
if (strncmp($string1, $string2, [1]) === 0) {
    echo "First 3 characters are equal.";
} else {
    echo "First 3 characters are different.";
}
?>

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

A2

B4

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 or 4 which compares wrong number of characters.

Confusing the argument with string length.

The third argument of strncmp is the number of characters to compare. To compare first 3 characters, use 3.

4fill in blank

hard

Fill both blanks to create an associative array with words as keys and their lengths as values, only for words longer than 4 characters.

PHP

<?php
$words = ["apple", "cat", "banana", "dog"];
$lengths = [
    [1] => strlen([2]) 
    for [1] in $words 
    if strlen([1]) > 4
];
?>

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

A$word

B$words

Cword

Dstrlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using $words which is the whole array, not a single word.

Using word without $ which is invalid in PHP.

Use $word as the variable name for each word in the array. It is used as key and inside strlen to get length.

5fill in blank

hard

Fill all three blanks to create an associative array with uppercase words as keys and their lengths as values, only for words longer than 3 characters.

PHP

<?php
$words = ["pear", "fig", "grape", "kiwi"];
$result = [
    [1] => [2] 
    for [3] in $words 
    if strlen([3]) > 3
];
?>

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

Astrtoupper($word)

Bstrlen($word)

C$word

D$fruit

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Not using strtoupper for the key.

Use $word as the variable name. The key is the uppercase word using strtoupper($word). The value is the length using strlen($word).

Practice

1. Which PHP function compares two strings in a case-sensitive way and returns 0 if they are exactly equal?

easy

A. strncmp

B. strcasecmp

C. strncasecmp

D. strcmp

Solution

1. Step 1: Understand case sensitivity in string comparison

   strcmp compares two strings exactly, including case.

2. Step 2: Identify function behavior

   strcmp returns 0 if strings are exactly equal, considering case.

3. Final Answer:

   strcmp -> Option D

4. Quick Check:

   Case-sensitive compare = strcmp [OK]

Hint: Case matters? Use strcmp or strncmp [OK]

Common Mistakes:

• Confusing strcmp with strcasecmp (case-insensitive)
• Using strncasecmp for full string compare
• Thinking strcmp ignores case

2. Which of the following is the correct syntax to compare first 3 characters of two strings ignoring case in PHP?

easy

A. strncasecmp($str1, $str2, 3)

B. strncmp($str1, $str2, 3)

C. strcasecmp($str1, $str2, 3)

D. strcmp($str1, $str2, 3)

Solution

1. Step 1: Identify function for case-insensitive partial compare

   strncasecmp compares first N characters ignoring case.

2. Step 2: Check syntax correctness

   strncasecmp($str1, $str2, 3) correctly compares first 3 chars case-insensitively.

3. Final Answer:

   strncasecmp($str1, $str2, 3) -> Option A

4. Quick Check:

   Partial case-insensitive compare = strncasecmp [OK]

Hint: Partial + ignore case = strncasecmp [OK]

Common Mistakes:

• Using strncmp which is case-sensitive
• Passing length to strcasecmp (no length param)
• Using strcmp with length parameter

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

$result = strcasecmp('Hello', 'hello');
echo $result;

medium

A. -1

B. 0

C. 1

D. Error

Solution

1. Step 1: Understand strcasecmp behavior

   It compares strings ignoring case and returns 0 if equal.

2. Step 2: Compare 'Hello' and 'hello'

   Ignoring case, both strings are equal, so result is 0.

3. Final Answer:

   0 -> Option B

4. Quick Check:

   strcasecmp('Hello', 'hello') = 0 [OK]

Hint: strcasecmp returns 0 if strings equal ignoring case [OK]

Common Mistakes:

• Expecting 1 or -1 for equal strings
• Confusing case-sensitive strcmp with strcasecmp
• Thinking it throws error for case differences

4. Identify the error in this PHP code snippet:

if (strncmp('apple', 'Apple', 5) == 0) {
    echo 'Match';
} else {
    echo 'No match';
}

medium

A. No error, code works correctly

B. Use strcasecmp instead of strncmp for case-insensitive compare

C. Use strncasecmp instead of strncmp for case-insensitive compare

D. Change 5 to length of shorter string

Solution

1. Step 1: Analyze strncmp behavior

   strncmp is case-sensitive, so 'apple' != 'Apple'.

2. Step 2: Fix for case-insensitive compare

   Use strncasecmp to ignore case in first 5 chars.

3. Final Answer:

   Use strncasecmp instead of strncmp for case-insensitive compare -> Option C

4. Quick Check:

   Case-insensitive partial compare needs strncasecmp [OK]

Hint: strncmp is case-sensitive; use strncasecmp to ignore case [OK]

Common Mistakes:

• Assuming strncmp ignores case
• Using strcasecmp with length parameter
• Changing length unnecessarily

5. You want to sort an array of strings alphabetically ignoring case in PHP. Which function is best to use as a comparison callback for usort?

hard

A. strcasecmp

B. strcmp

C. strncmp

D. strncasecmp

Solution

1. Step 1: Understand sorting with case-insensitivity

   Sorting ignoring case requires a case-insensitive comparison function.

2. Step 2: Choose correct function for full string compare ignoring case

   strcasecmp compares full strings ignoring case, ideal for sorting.

3. Final Answer:

   strcasecmp -> Option A

4. Quick Check:

   Case-insensitive full compare for sorting = strcasecmp [OK]

Hint: Sort ignoring case? Use strcasecmp as callback [OK]

Common Mistakes:

• Using strcmp which is case-sensitive
• Using strncmp or strncasecmp which compare partial strings
• Passing no callback to usort