Variable naming rules in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

PHP Variable Naming: Output Check

What is the output of this PHP code snippet?

PHP

<?php
$var1 = 10;
$_var2 = 20;
$3var = 30;
echo $var1 + $_var2;
?>

A Syntax error

B 30

C 50

D Notice: Undefined variable

💡 Hint

Remember PHP variable names cannot start with a number.

In PHP, variable names must start with a letter or underscore. $3var starts with a digit, causing a syntax error.

❓ Predict Output

intermediate

PHP Variable Naming: Case Sensitivity

What will be the output of this PHP code?

PHP

<?php
$Var = 5;
$var = 10;
echo $Var + $var;
?>

A 15

B 10

C 5

D Undefined variable error

💡 Hint

PHP variable names are case sensitive.

PHP treats $Var and $var as two different variables. So 5 + 10 = 15.

❓ Predict Output

advanced

PHP Variable Naming: Valid or Invalid?

Which variable name is invalid in PHP?

A $_userName

B $user_name

C $user-name

D $UserName123

💡 Hint

PHP variable names cannot contain hyphens.

Hyphens are not allowed in PHP variable names because they are interpreted as minus operators.

❓ Predict Output

advanced

PHP Variable Naming: Output Prediction

What will this PHP code output?

PHP

<?php
$var = 1;
$Var = 2;
$VAR = 3;
echo $var + $Var + $VAR;
?>

A 1

B 3

C Undefined variable error

D 6

💡 Hint

PHP variable names are case sensitive.

Each variable is distinct: 1 + 2 + 3 = 6.

❓ Predict Output

expert

PHP Variable Naming: Complex Output

What is the output of this PHP code?

PHP

<?php
$var = 5;
$var_2 = 10;
$var2 = 15;
echo $var + $var_2 + $var2;
?>

A Syntax error

B 30

C 25

D Undefined variable error

💡 Hint

Underscores and numbers are allowed in variable names as long as they don't start with a number.

All three variables are valid and distinct. Their sum is 5 + 10 + 15 = 30.

Practice

1. Which of the following is a valid variable name in PHP?

easy

A. $user_name

B. 2ndUser

C. user-name

D. user name

Solution

1. Step 1: Check the first character of each variable

   PHP variables must start with a $ followed by a letter or underscore, not a number or space.

2. Step 2: Validate allowed characters

   Variable names can only contain letters, numbers, and underscores after the $. Spaces and hyphens are not allowed.

3. Final Answer:

   $user_name -> Option A

4. Quick Check:

   Starts with $ and uses letters/underscore [OK]

Hint: Variable names start with $ and no spaces or hyphens [OK]

Common Mistakes:

• Starting variable with a number
• Using spaces or hyphens in variable names
• Omitting the $ sign at the start

2. Which of these variable declarations will cause a syntax error in PHP?

easy

A. $totalAmount = 100;

B. $_count = 5;

C. $9value = 10;

D. $userName = 'John';

Solution

1. Step 1: Identify the variable starting characters

   PHP variables must start with $ followed by a letter or underscore, not a number.

2. Step 2: Check each option

   Options B, C, and D start correctly. $9value = 10; starts with $9, which is invalid.

3. Final Answer:

   Syntax error due to starting with a number -> Option C

4. Quick Check:

   Variable cannot start with number [OK]

Hint: Variables cannot start with numbers, only letters or _ after $ [OK]

Common Mistakes:

• Starting variable names with digits
• Confusing variable names with constants
• Missing the $ sign

3. What will be the output of the following PHP code?

$Var = 10;
$var = 20;
echo $Var + $var;

medium

A. 20

B. 30

C. 10

D. Error

Solution

1. Step 1: Understand variable case sensitivity in PHP

   PHP variable names are case-sensitive, so $Var and $var are different variables.

2. Step 2: Calculate the sum of both variables

   $Var is 10 and $var is 20, so their sum is 30.

3. Final Answer:

   30 -> Option B

4. Quick Check:

   Case-sensitive variables sum correctly [OK]

Hint: PHP variables are case-sensitive; $Var and $var differ [OK]

Common Mistakes:

• Assuming variables with different cases are the same
• Expecting a syntax error due to case difference
• Ignoring case sensitivity in variable names

4. Identify the error in this PHP code:

$1stName = 'Alice';
$lastName = 'Smith';
echo $1stName . ' ' . $lastName;

medium

A. Variable names cannot contain uppercase letters

B. Missing semicolon after echo statement

C. Concatenation operator is incorrect

D. Variable names cannot start with a number

Solution

1. Step 1: Check variable naming rules

   Variable names cannot start with a number. $1stName starts with '1', which is invalid.

2. Step 2: Verify other parts of the code

   The concatenation operator . and semicolons are correct, and uppercase letters are allowed.

3. Final Answer:

   Variable names cannot start with a number -> Option D

4. Quick Check:

   Variable names must start with letter or _ [OK]

Hint: Variable names cannot start with digits, only letters or underscore [OK]

Common Mistakes:

• Thinking uppercase letters are invalid
• Confusing concatenation operator with plus sign
• Missing semicolons causing errors

5. You want to store a user's age in a variable. Which variable name follows PHP naming rules and is the clearest choice?

hard

A. $userAge

B. $user-age

C. $age user

D. $2age

Solution

1. Step 1: Check PHP variable naming rules

   Variable names must start with $ followed by a letter or underscore, and can contain letters, numbers, and underscores only.

2. Step 2: Evaluate clarity and correctness of options

   $userAge uses camelCase with allowed characters. Options A and B contain hyphens and spaces, which are invalid. $2age starts with a number, which is invalid.

3. Final Answer:

   $userAge -> Option A

4. Quick Check:

   Clear, valid variable name with letters and no invalid characters [OK]

Hint: Use letters and underscores, no spaces or hyphens, start with $ [OK]

Common Mistakes:

• Using spaces or hyphens in variable names
• Starting variable names with numbers
• Choosing unclear or confusing names