String comparison functions in PHP - Step-by-Step Execution

Concept Flow - String comparison functions

Start

↓

Get two strings

↓

Choose comparison function

↓

Compare strings

↓

Return comparison result

↓

Use result to decide next step

↓

End

The program gets two strings, compares them using a chosen function, then returns and uses the result.

Execution Sample

PHP

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

Compares two strings 'apple' and 'banana' using strcmp and prints the result.

Execution Table

Step	Action	Input Strings	Function Called	Return Value	Meaning
1	Initialize strings	$str1 = 'apple', $str2 = 'banana'	N/A	N/A	Strings ready for comparison
2	Call strcmp	'apple', 'banana'	strcmp	-1	'apple' is less than 'banana'
3	Print result	N/A	N/A	-1	Output is -1 showing order
4	End	N/A	N/A	N/A	Program ends

💡 All steps completed, comparison result printed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$str1	undefined	apple	apple	apple	apple
$str2	undefined	banana	banana	banana	banana
$result	undefined	undefined	-1	-1	-1

Key Moments - 3 Insights

Why does strcmp return -1 instead of true or false?

strcmp returns an integer: negative if first string is less, zero if equal, positive if greater. See execution_table step 2 where -1 means 'apple' is less than 'banana'.

What happens if strings are equal?

If strings are equal, strcmp returns 0. This is shown by the return value meaning in execution_table step 2.

Why not use == to compare strings?

Using == checks equality only, but strcmp gives order info (less, equal, greater). This helps in sorting or ordering decisions.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of $result after step 2?

A 0

B -1

C 1

D undefined

💡 Hint

Check the 'Return Value' column in execution_table row for step 2.

At which step does the program print the comparison result?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look for the 'Print result' action in execution_table.

If $str1 was 'banana' and $str2 was 'apple', what would strcmp return?

A 1

B 0

C -1

D undefined

💡 Hint

strcmp returns positive if first string is greater; see meaning column in execution_table step 2.

Concept Snapshot

PHP string comparison functions:
- strcmp(str1, str2): returns <0 if str1 < str2, 0 if equal, >0 if str1 > str2
- Useful for sorting or ordering strings
- Returns integer, not boolean
- Use === or == for equality only

Full Transcript

This example shows how PHP compares two strings using strcmp. First, two strings are set: 'apple' and 'banana'. Then strcmp is called with these strings. It returns -1 because 'apple' comes before 'banana' alphabetically. The program prints this result. strcmp returns an integer indicating order: negative means first string is less, zero means equal, positive means greater. This helps decide string order, unlike simple equality checks. The execution table tracks each step and variable values. Beginners often confuse strcmp's return values with true/false, but it actually returns an integer to show order. This is important for sorting or comparing strings beyond equality.

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