Common validation patterns in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a variable is set.

PHP

<?php
if ([1](
  $name
)) {
  echo "Name is set.";
} else {
  echo "Name is not set.";
}
?>

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

Aisset

Bempty

Cis_null

Dis_string

Attempts:

3 left

💡 Hint

Common Mistakes

Using empty() which returns true if the variable is empty, not just set.

Using is_null() which checks if variable is null but does not check if it is set.

The isset function checks if a variable is set and is not null.

2fill in blank

medium

Complete the code to validate if a string contains only digits.

PHP

<?php
if ([1]($input)) {
  echo "Input is numeric.";
} else {
  echo "Input is not numeric.";
}
?>

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

Ais_numeric

Bis_string

Cctype_digit

Dpreg_match

Attempts:

3 left

💡 Hint

Common Mistakes

Using is_numeric() which allows decimal points and signs.

Using preg_match without a proper pattern.

The ctype_digit function checks if all characters in the string are digits.

3fill in blank

hard

Fix the error in the code to validate an email address.

PHP

<?php
$email = "[e-mail]";
if (filter_var($email, [1])) {
  echo "Valid email.";
} else {
  echo "Invalid email.";
}
?>

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

AFILTER_VALIDATE_INT

BFILTER_DEFAULT

CFILTER_SANITIZE_EMAIL

DFILTER_VALIDATE_EMAIL

Attempts:

3 left

💡 Hint

Common Mistakes

Using FILTER_SANITIZE_EMAIL which only cleans the email but does not validate.

Using FILTER_VALIDATE_INT which is for integers.

FILTER_VALIDATE_EMAIL is used with filter_var to check if the email is valid.

4fill in blank

hard

Fill both blanks to create an array of words longer than 3 characters.

PHP

<?php
$words = ['cat', 'house', 'dog', 'elephant'];
$longWords = array_filter($words, function($word) {
  return strlen($word) [1] [2];
});
print_r($longWords);
?>

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

A>

B<

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' causing wrong filtering.

Using 5 instead of 3 changing the condition.

The code filters words with length greater than 3 using strlen($word) > 3.

5fill in blank

hard

Fill all three blanks to create an associative array of words and their lengths for words longer than 4.

PHP

<?php
$words = ['apple', 'bat', 'carrot', 'dog'];
$lengths = array_filter(array_combine(
  array_map(function($word) { return [1]; }, $words),
  array_map(function($word) { return [2]; }, $words)
), function($len) { return $len [3] 4; });
print_r($lengths);
?>

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

A$word

Bstrlen($word)

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the filter condition.

Using wrong variable names in map functions.

The code maps words as keys and their lengths as values, then filters lengths greater than 4.

Practice

1.

Which PHP function is commonly used to validate if a string is a valid email address?

easy

A. preg_match with '/^\d+$/'

B. filter_var with FILTER_VALIDATE_EMAIL

C. strlen to check length

D. strtolower to convert to lowercase

Solution

1. Step 1: Understand email validation in PHP

   PHP provides a built-in filter called FILTER_VALIDATE_EMAIL to check if a string is a valid email.

2. Step 2: Identify the correct function usage

   filter_var with FILTER_VALIDATE_EMAIL returns the email if valid, or false if invalid.

3. Final Answer:

   filter_var with FILTER_VALIDATE_EMAIL -> Option B

4. Quick Check:

   Email validation = filter_var with FILTER_VALIDATE_EMAIL [OK]

Hint: Use filter_var with FILTER_VALIDATE_EMAIL for email checks [OK]

Common Mistakes:

• Using preg_match with wrong regex for email
• Checking length instead of format
• Using string functions unrelated to validation

2.

Which of the following is the correct syntax to validate a URL using filter_var in PHP?

?

easy

A. filter_var($url, FILTER_VALIDATE_INT);

B. filter_var($url, FILTER_VALIDATE_EMAIL);

C. filter_var($url, FILTER_VALIDATE_URL);

D. filter_var($url, FILTER_VALIDATE_BOOLEAN);

Solution

1. Step 1: Identify the filter for URL validation

   FILTER_VALIDATE_URL is the correct filter to check if a string is a valid URL.

2. Step 2: Confirm correct function call

   filter_var takes the variable and the filter constant as parameters.

3. Final Answer:

   filter_var($url, FILTER_VALIDATE_URL); -> Option C

4. Quick Check:

   URL validation = filter_var with FILTER_VALIDATE_URL [OK]

Hint: Use FILTER_VALIDATE_URL with filter_var for URL validation [OK]

Common Mistakes:

• Using FILTER_VALIDATE_EMAIL for URLs
• Using integer or boolean filters incorrectly
• Missing the filter parameter

3.

What will be the output of the following PHP code?

$phone = '123-456-7890';
if (preg_match('/^\d{3}-\d{3}-\d{4}$/', $phone)) {
    echo 'Valid phone';
} else {
    echo 'Invalid phone';
}

medium

A. Syntax error

B. Invalid phone

C. No output

D. Valid phone

Solution

1. Step 1: Analyze the regex pattern

   The pattern /^\d{3}-\d{3}-\d{4}$/ matches exactly 3 digits, a dash, 3 digits, a dash, then 4 digits.

2. Step 2: Check the input string against the pattern

   The string '123-456-7890' matches this pattern exactly.

3. Final Answer:

   Valid phone -> Option D

4. Quick Check:

   Regex matches phone format = Valid phone [OK]

Hint: Match exact pattern with preg_match regex anchors ^ and $ [OK]

Common Mistakes:

• Forgetting anchors ^ and $ in regex
• Using wrong quantifiers in regex
• Not escaping special characters

4.

Identify the error in this PHP code snippet for validating an integer:

$num = '123a';
if (filter_var($num, FILTER_VALIDATE_INT)) {
    echo 'Valid integer';
} else {
    echo 'Invalid integer';
}

medium

A. filter_var returns false for '123a', so output is 'Invalid integer'

B. filter_var should use FILTER_VALIDATE_NUMBER instead

C. The variable $num should be cast to int before validation

D. filter_var does not validate integers

Solution

1. Step 1: Understand filter_var with FILTER_VALIDATE_INT

   This filter returns the integer value if valid, or false if invalid.

2. Step 2: Check input '123a'

   The string '123a' is not a valid integer, so filter_var returns false.

3. Final Answer:

   filter_var returns false for '123a', so output is 'Invalid integer' -> Option A

4. Quick Check:

   Invalid integer string returns false = 'Invalid integer' output [OK]

Hint: filter_var returns false if input is not a pure integer string [OK]

Common Mistakes:

• Using FILTER_VALIDATE_NUMBER which does not exist
• Casting before validation causing wrong results
• Assuming filter_var always returns boolean

5.

You want to validate a username in PHP that must start with a letter, can contain letters, numbers, underscores, and be 5 to 15 characters long. Which preg_match pattern correctly validates this?

hard

A. /^[a-zA-Z][a-zA-Z0-9_]{4,14}$/

B. /^[0-9][a-zA-Z0-9_]{4,14}$/

C. /^[a-zA-Z0-9_]{5,15}$/

D. /^[a-zA-Z]{5,15}$/

Solution

1. Step 1: Understand username requirements

   Username must start with a letter, then 4 to 14 characters of letters, digits, or underscores, total length 5-15.

2. Step 2: Analyze each pattern

   /^[a-zA-Z][a-zA-Z0-9_]{4,14}$/ matches a letter at start, then 4-14 allowed chars, total 5-15 length. Others fail start or length rules.

3. Final Answer:

   /^[a-zA-Z][a-zA-Z0-9_]{4,14}$/ -> Option A

4. Quick Check:

   Start letter + allowed chars + length 5-15 = /^[a-zA-Z][a-zA-Z0-9_]{4,14}$/ [OK]

Hint: Start with letter, then allowed chars with correct length in regex [OK]

Common Mistakes:

• Allowing digits as first character
• Not enforcing length limits
• Missing anchors ^ and $