String comparison functions in PHP - Mini Project: Build & Apply

String comparison functions

📖 Scenario: You are building a simple PHP program to compare two strings in different ways. This is useful when you want to check if two words are the same, or if one word comes before another in alphabetical order.

🎯 Goal: Create a PHP script that compares two strings using different string comparison functions and shows the results.

📋 What You'll Learn

Create two string variables with exact values

Create a variable to hold the length limit for comparison

Use strcmp to compare the two strings

Use strcasecmp to compare the two strings ignoring case

Use strncmp to compare the first N characters of the two strings

Print the results of all comparisons

💡 Why This Matters

🌍 Real World

String comparison is important in many programs like sorting names, checking passwords, or filtering text.

💼 Career

Understanding string comparison functions helps in data validation, search features, and user input handling in web development.

1

DATA SETUP: Create two string variables

Create two string variables called string1 and string2 with these exact values: "HelloWorld" and "helloworld" respectively.

PHP

// Your code here

Hint

Use the = sign to assign the exact text to each variable.

2

CONFIGURATION: Create a length variable for partial comparison

Create an integer variable called length and set it to 5.

PHP

<?php
$string1 = "HelloWorld";
$string2 = "helloworld";
// Your code here

Hint

Just create a variable with the number 5 to use later.

3

CORE LOGIC: Compare the strings using string comparison functions

Use strcmp to compare $string1 and $string2 and store the result in $result1. Then use strcasecmp to compare $string1 and $string2 ignoring case and store in $result2. Finally, use strncmp to compare the first $length characters of $string1 and $string2 and store in $result3.

PHP

<?php
$string1 = "HelloWorld";
$string2 = "helloworld";
$length = 5;
// Your code here

Hint

Use the exact function names and variable names as shown.

4

OUTPUT: Print the comparison results

Print the values of $result1, $result2, and $result3 each on a new line using echo.

PHP

<?php
$string1 = "HelloWorld";
$string2 = "helloworld";
$length = 5;

$result1 = strcmp($string1, $string2);
$result2 = strcasecmp($string1, $string2);
$result3 = strncmp($string1, $string2, $length);
// Your code here

Hint

Use echo and add a newline character \n after each result.

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