String comparison functions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of strcmp with different cases

What is the output of this PHP code snippet?

PHP

<?php
$str1 = "Hello";
$str2 = "hello";
$result = strcmp($str1, $str2);
echo $result;
?>

A 0

B 1

C -32

D SyntaxError

💡 Hint

strcmp compares strings byte by byte and is case-sensitive.

The strcmp function compares two strings in a case-sensitive way. Since uppercase 'H' has a lower ASCII value (72) than lowercase 'h' (104), the result is 72 - 104 = -32.

❓ Predict Output

intermediate

Output of strcasecmp with different cases

What will this PHP code output?

PHP

<?php
$str1 = "World";
$str2 = "world";
$result = strcasecmp($str1, $str2);
echo $result;
?>

A 0

B -1

C Warning: Undefined function

D 1

💡 Hint

strcasecmp compares strings ignoring case differences.

The strcasecmp function compares two strings ignoring case. Since "World" and "world" differ only in case, the result is 0, meaning they are equal.

❓ Predict Output

advanced

Behavior of strncmp with partial string comparison

What is the output of this PHP code?

PHP

<?php
$str1 = "apple";
$str2 = "apples";
$result = strncmp($str1, $str2, 5);
echo $result;
?>

A -1

B 0

C 1

D Fatal error

💡 Hint

strncmp compares only the first n characters of two strings.

The strncmp function compares only the first 5 characters: "apple" and "apple" (from "apples"), which are identical, so the result is 0.

❓ Predict Output

advanced

Output of substr_compare with offset and length

What does this PHP code output?

PHP

<?php
$str1 = "abcabc";
$str2 = "xyzabc";
$result = substr_compare($str1, $str2, 3, 3);
echo $result;
?>

A Warning: Wrong parameters

B 0

C 23

D -23

💡 Hint

substr_compare compares substrings starting at offset for given length.

The substrings compared are from offset 3 with length 3: "abc" from $str1 and "abc" from $str2 (starting at position 3).

Comparing 'a' (ASCII 97) and 'a' (ASCII 97), the difference is 0.

🧠 Conceptual

expert

Which function is best for case-insensitive string comparison with offset?

You want to compare two strings ignoring case, starting at a specific position and for a specific length. Which PHP function should you use?

A strncasecmp

B strncmp

C substr_compare

D strcasecmp

💡 Hint

Look for a function that combines case-insensitive, length-limited, and offset-based comparison.

strncasecmp performs case-insensitive comparison up to a specified length (but starts from the beginning of strings). For offset, substr() can be used first. substr_compare supports offset/length but is case-sensitive unless the optional case-insensitivity flag is set. Among options, strncasecmp fits case-insensitive partial comparison best.

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