String comparison functions in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the PHP function strcmp() do?

strcmp() compares two strings exactly and returns:

• 0 if both strings are equal
• A negative number if the first string is less than the second
• A positive number if the first string is greater than the second

beginner

How is strcasecmp() different from strcmp()?

strcasecmp() compares two strings ignoring case differences, while strcmp() is case-sensitive.

intermediate

What does strncmp() do in PHP?

strncmp() compares up to a specified number of characters from two strings. It returns 0 if the compared parts are equal.

beginner

Explain the return values of strcmp() with an example.

Example: strcmp('apple', 'banana') returns a negative number because 'apple' is less than 'banana' alphabetically.

Return values:

• 0 if equal
• <0 if first string < second string
• >0 if first string > second string

beginner

Why use strcasecmp() instead of strcmp()?

Use strcasecmp() when you want to compare strings without caring about uppercase or lowercase letters, like comparing user input where case should not matter.

What does strcmp('Hello', 'hello') return?

A 0

B A positive number

C A negative number

D Boolean true

strcmp() is case-sensitive. 'H' (uppercase) is less than 'h' (lowercase) in ASCII, so it returns a negative number.

Which function compares strings ignoring case?

A strcasecmp()

B strncmp()

C strcmp()

D strncasecmp()

strcasecmp() compares strings ignoring case differences.

What does strncmp('apple', 'apricot', 3) return?

A Boolean false

B Positive number

C Negative number

D 0

It compares first 3 characters: 'app' vs 'apr'. Since 'app' and 'apr' differ at the third character, 'p' vs 'r', 'p' is less than 'r', so it returns a negative number.

Which function compares only the first N characters of two strings?

A strncmp()

B strcmp()

C strcasecmp()

D str_replace()

strncmp() compares up to N characters of two strings.

If strcmp($a, $b) returns 0, what does it mean?

A $a is less than $b

B $a and $b are equal

C $a is greater than $b

D Comparison failed

A return value of 0 means both strings are exactly equal.

Describe how strcmp() works and what its return values mean.

Think about how two words are ordered in a dictionary.

When would you use strcasecmp() instead of strcmp()?

Consider comparing names or emails where uppercase and lowercase letters should not matter.