Variable declaration with dollar sign in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What symbol is used to declare a variable in PHP?

In PHP, variables are declared using the dollar sign $ before the variable name, like $variableName.

beginner

Why does PHP use a dollar sign $ before variable names?

The dollar sign $ tells PHP that what follows is a variable. It helps PHP recognize variables easily in the code.

beginner

Is this a valid PHP variable declaration?
$name = "Alice";

Yes, this is valid. The variable $name is declared and assigned the string value "Alice".

beginner

Can variable names in PHP start with a number? For example, is $1name valid?

No, variable names cannot start with a number. They must start with a letter or underscore after the dollar sign.

beginner

How do you declare multiple variables in PHP using the dollar sign?

You declare each variable with its own dollar sign, for example: $a = 1; $b = 2;. Each variable needs its own $.

What does the dollar sign $ mean in PHP variable declaration?

A It marks the start of a variable name

B It is used for comments

C It declares a function

D It ends a statement

The dollar sign $ tells PHP that the following word is a variable name.

Which of these is a valid PHP variable name?

A $2ndPlace

B $_score

C $-value

D $ name

Variable names must start with a letter or underscore after the dollar sign. $_score is valid.

How do you assign the number 10 to a variable named count in PHP?

A $count = 10;

B #count = 10;

C var count = 10;

D count = 10;

In PHP, variables start with $, so $count = 10; is correct.

What will this PHP code output?
$name = "Bob"; echo $name;

A name

B $name

C Bob

D Error

The variable $name holds "Bob", so echo prints "Bob".

Can you declare two variables like this in PHP?
$a = 5, $b = 10;

A Only if inside a function

B No, variables must be declared on separate lines

C No, commas are not allowed in variable declarations

D Yes, this is valid syntax

Yes, this is valid syntax. You can declare multiple variables separated by commas like $a = 5, $b = 10;.

Explain how to declare a variable in PHP and why the dollar sign is necessary.

Think about how PHP knows something is a variable.

Describe the rules for naming variables in PHP after the dollar sign.

Consider what characters are allowed at the start and inside variable names.

Practice

1. Which of the following is the correct way to declare a variable named age in PHP?

easy

A. $age = 25;

B. age = 25;

C. var age = 25;

D. int $age = 25;

Solution

1. Step 1: Recognize PHP variable syntax

   In PHP, all variables must start with a dollar sign ($) followed by the variable name.

2. Step 2: Check each option for correct syntax

   $age = 25; uses $age = 25; which is correct. Options B and C miss the dollar sign, and A uses a type declaration which is not standard in PHP variable declaration.

3. Final Answer:

   $age = 25; -> Option A

4. Quick Check:

   PHP variables start with $ = $age = 25; [OK]

Hint: Always start PHP variables with $ sign [OK]

Common Mistakes:

• Forgetting the $ sign before variable name
• Using other language syntax like var or int
• Trying to declare type explicitly in PHP

2. Which of the following is a syntax error in PHP variable declaration?

easy

A. $1number = 10;

B. $name = "John";

C. $total = 100;

D. $_score = 50;

Solution

1. Step 1: Understand valid variable names in PHP

   Variable names must start with a letter or underscore, not a number.

2. Step 2: Identify invalid variable name

   $1number = 10; uses $1number which starts with a number, causing a syntax error. Other options start with $ followed by letter or underscore, which is valid.

3. Final Answer:

   $1number = 10; -> Option A

4. Quick Check:

   Variable names cannot start with digits = $1number = 10; [OK]

Hint: Variable names cannot start with numbers [OK]

Common Mistakes:

• Starting variable names with digits
• Using spaces in variable names
• Using special characters other than underscore

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

$x = 5;
$y = $x;
$x = 10;
echo $y;

medium

A. Error

B. 10

C. 0

D. 5

Solution

1. Step 1: Understand variable assignment in PHP

   When $y = $x; runs, $y gets the current value of $x, which is 5.

2. Step 2: Check effect of changing $x after assignment

   Changing $x to 10 later does not affect $y because $y holds a copy of the value, not a reference.

3. Final Answer:

   5 -> Option D

4. Quick Check:

   Variable copy keeps old value = 5 [OK]

Hint: Variable assignment copies value, not reference [OK]

Common Mistakes:

• Assuming $y changes when $x changes
• Confusing references with copies
• Expecting runtime error for reassignment

4. Identify the error in this PHP code snippet:

$var1 = 10;
var2 = 20;
echo $var2;

medium

A. echo statement syntax error

B. Missing $ sign before var2

C. Missing semicolon after var1

D. Variable names cannot have numbers

Solution

1. Step 1: Check variable declarations

   $var1 is declared correctly with a $ sign. var2 is missing the $ sign, which is required in PHP.

2. Step 2: Analyze the echo statement

   echo uses $var2 which is undefined because var2 was not declared properly.

3. Final Answer:

   Missing $ sign before var2 -> Option B

4. Quick Check:

   All PHP variables need $ sign = Missing $ sign before var2 [OK]

Hint: Every PHP variable must start with $ [OK]

Common Mistakes:

• Forgetting $ sign before variable
• Assuming semicolon missing causes error here
• Thinking numbers are not allowed in variable names

5. You want to store a user's first name and age in PHP variables and then display them. Which code correctly declares and uses these variables?

1. $firstName = "Alice";
2. $age = 30;
3. echo "Name: $firstName, Age: $age";

hard

A. Declare variables without $ sign and use $ in echo

B. Use variables without $ sign in echo: echo "Name: firstName, Age: age";

C. Declare variables with $ and use them with $ in echo as shown

D. Use $ only in declaration, not in echo

Solution

1. Step 1: Declare variables with $ sign

   Lines 1 and 2 correctly declare variables $firstName and $age with $ sign.

2. Step 2: Use variables with $ sign inside double quotes

   In PHP, variables inside double quotes are parsed and replaced with their values, so echo "Name: $firstName, Age: $age"; works correctly.

3. Final Answer:

   Declare variables with $ and use them with $ in echo as shown -> Option C

4. Quick Check:

   Variables need $ in declaration and usage [OK]

Hint: Use $ sign in both declaration and usage [OK]

Common Mistakes:

• Omitting $ sign in echo
• Using single quotes which don't parse variables
• Declaring variables without $ sign