Variable naming rules in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What character must a PHP variable name start with?

A PHP variable name must start with a dollar sign ($). For example, $variable is valid.

beginner

Can PHP variable names contain spaces or special characters like @ or #?

No, PHP variable names cannot contain spaces or special characters like @ or #. They can only contain letters, numbers, and underscores after the initial $.

beginner

Are PHP variable names case-sensitive?

Yes, PHP variable names are case-sensitive. For example, $Name and $name are two different variables.

beginner

Is $2ndValue a valid PHP variable name? Why or why not?

No, $2ndValue is not valid because variable names cannot start with a number after the dollar sign. The first character after $ must be a letter or underscore.

beginner

What characters are allowed in PHP variable names after the initial $?

After the initial $, PHP variable names can contain letters (a-z, A-Z), numbers (0-9), and underscores (_). They cannot start with a number.

Which of the following is a valid PHP variable name?

A $user_name

B userName

C $9lives

D $user-name

Only option C is valid. It starts with $ followed by a letter or underscore, and uses only allowed characters (letters, numbers, and underscore). A starts with a number after $, B lacks $, and D contains a hyphen.

Are PHP variable names case-sensitive?

A Only in some PHP versions

B No, $Var and $var are the same variable

C Yes, $Var and $var are different variables

D Only for variables starting with underscore

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

What is the first character of every PHP variable name?

A $

B _

C a letter

D a number

Every PHP variable name must start with a dollar sign ($).

Which character is NOT allowed in PHP variable names after the $?

A a

B 9

C _

D -

Hyphens (-) are not allowed in PHP variable names.

Is this variable name valid in PHP? $_myVar123

A No, because it contains uppercase letters

B Yes

C No, because it contains numbers

D No, because it starts with underscore

Variable names can start with an underscore and contain numbers and uppercase letters.

Explain the rules for naming variables in PHP.

Think about what characters are allowed and the importance of the $ sign.

Why is $2ndValue not a valid variable name in PHP? What would be a valid alternative?

Focus on the first character after the dollar sign.

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