Variable scope in functions in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is variable scope in PHP functions?

Variable scope defines where a variable can be accessed or used in the code. In PHP, variables inside functions are local by default and cannot be accessed outside the function.

beginner

What happens if you try to use a variable declared outside a function inside that function without any special keyword?

The function will not see the outside variable because variables inside functions are local by default. You need to use the global keyword or pass the variable as a parameter to access it.

beginner

How do you access a global variable inside a PHP function?

Use the global keyword inside the function before the variable name. This tells PHP to use the variable from the global scope.

intermediate

What is the static keyword used for in PHP functions?

The static keyword keeps a local variable's value between function calls. It means the variable does not reset each time the function runs.

beginner

Explain the difference between local and global variables in PHP.

Local variables exist only inside the function where they are declared. Global variables exist outside functions and can be accessed anywhere if declared global inside functions.

What keyword allows a function to access a variable declared outside it?

A global

B local

C static

D public

The global keyword tells the function to use the variable from the global scope.

What is the scope of a variable declared inside a function without any keyword?

A Global

B Public

C Static

D Local

Variables declared inside functions are local to that function by default.

Which keyword keeps a variable's value between function calls?

A global

B local

C static

D const

The static keyword preserves the variable's value between calls.

If you want to use a global variable inside a function without global, what is a good alternative?

A Pass it as a function parameter

B Declare it again inside the function

C Use <code>static</code> keyword

D Use <code>const</code> keyword

Passing the variable as a parameter lets the function use its value without needing global.

What happens if you try to access a local variable outside its function?

A It works fine

B It causes an error or undefined variable

C It accesses the global variable

D It converts to static

Local variables only exist inside their function and cannot be accessed outside.

Explain how variable scope works inside PHP functions and how to access variables from outside the function.

Think about where variables live and how to share them with functions.

Describe the purpose of the static keyword in PHP functions and give an example of when it might be useful.

Consider a counter that remembers its value each time a function runs.

Practice

1. What is the scope of a variable declared inside a PHP function without using global?

easy

A. It is accessible only outside the function.

B. It is global and accessible everywhere.

C. It is static and retains value between calls.

D. It is local to the function only.

Solution

1. Step 1: Understand variable declaration inside functions

   Variables declared inside a function are local by default, meaning they exist only within that function.

2. Step 2: Recall the role of the global keyword

   Without using global, the variable does not refer to any global variable with the same name.

3. Final Answer:

   It is local to the function only. -> Option D

4. Quick Check:

   Local scope = inside function only [OK]

Hint: Variables inside functions are local unless declared global [OK]

Common Mistakes:

• Assuming variables inside functions are global by default
• Confusing local variables with static variables
• Thinking variables inside functions affect global variables automatically

2. Which of the following is the correct way to access a global variable $count inside a PHP function?

easy

A. Use var $count; inside the function.

B. Declare $count again inside the function.

C. Use global $count; inside the function.

D. Use static $count; inside the function.

Solution

1. Step 1: Recall how to access global variables inside functions

   In PHP, to access a global variable inside a function, you must declare it with the global keyword inside that function.

2. Step 2: Check other options for correctness

   Declaring the variable again inside the function creates a new local variable. static keeps value between calls but does not access global. var is not used inside functions.

3. Final Answer:

   Use global $count; inside the function. -> Option C

4. Quick Check:

   Access global with global keyword [OK]

Hint: Use 'global' keyword to access global variables inside functions [OK]

Common Mistakes:

• Re-declaring global variables inside functions without 'global'
• Using 'static' instead of 'global' to access globals
• Using 'var' keyword inside functions

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

$x = 5;
function test() {
    $x = 10;
    echo $x;
}
test();
echo $x;

medium

A. 10 5

B. 5 10

C. 10 10

D. 5 5

Solution

1. Step 1: Analyze variable scope inside the function

   Inside test(), $x is assigned 10 locally, so echo $x; prints 10.

2. Step 2: Analyze variable outside the function

   Outside the function, $x remains 5 because the local $x inside the function does not affect the global $x.

3. Final Answer:

   10 5 -> Option A

4. Quick Check:

   Local $x = 10, global $x = 5 [OK]

Hint: Local variables inside functions do not change globals [OK]

Common Mistakes:

• Assuming function changes global variable without 'global' keyword
• Confusing output order
• Thinking variables inside functions share the same memory as globals

4. Identify the error in the following PHP code and select the correct fix:

$count = 0;
function increment() {
    $count++;
}
increment();
echo $count;

medium

A. Declare $count as static inside the function.

B. Add global $count; inside the function.

C. Pass $count as a parameter to the function.

D. No error; code works fine.

Solution

1. Step 1: Understand variable scope in the function

   The function tries to increment $count, but without global, it treats $count as undefined local variable.

2. Step 2: Fix the scope issue

   Adding global $count; inside the function tells PHP to use the global $count variable, allowing increment to work.

3. Final Answer:

   Add global $count; inside the function. -> Option B

4. Quick Check:

   Use global keyword to modify global variables inside functions [OK]

Hint: Use 'global' to modify global variables inside functions [OK]

Common Mistakes:

• Forgetting to declare global variables inside functions
• Assuming variables are automatically global
• Using static instead of global for global variables

5. Consider the following PHP code:

$value = 3;
function multiply() {
    global $value;
    $value *= 2;
}
multiply();
function reset() {
    $value = 0;
}
reset();
echo $value;

What will be the output and why?

hard

A. 6 because multiply changes global, reset changes local only.

B. 0 because reset changes global variable.

C. 3 because multiply and reset do not affect global variable.

D. Error because reset tries to access undefined global variable.

Solution

1. Step 1: Analyze multiply() function

   It uses global $value; and doubles the global $value from 3 to 6.

2. Step 2: Analyze reset() function

   It declares $value without global, so it creates a local variable $value set to 0, leaving global $value unchanged.

3. Step 3: Final output

   After calling both functions, global $value remains 6, so echo $value; prints 6.

4. Final Answer:

   6 because multiply changes global, reset changes local only. -> Option A

5. Quick Check:

   global keyword affects global variable, local does not [OK]

Hint: Only functions with 'global' keyword affect global variables [OK]

Common Mistakes:

• Assuming reset() changes global variable without 'global'
• Thinking variables inside functions always affect globals
• Confusing local and global variable effects