Variable scope in functions in PHP - Mini Project: Build & Apply

Variable scope in functions

📖 Scenario: Imagine you are managing a small shop's sales system. You want to keep track of the total sales amount and update it when a new sale happens. But you need to understand how variables inside and outside functions behave.

🎯 Goal: You will create a variable to hold the total sales, write a function to add a sale amount, and learn how variable scope works in PHP functions.

📋 What You'll Learn

Create a variable called $totalSales and set it to 0

Create a variable called $newSale and set it to 150

Write a function called addSale that takes one parameter $amount

Inside addSale, add $amount to $totalSales using the global keyword

Call the function addSale with $newSale

Print the value of $totalSales after the function call

💡 Why This Matters

🌍 Real World

Understanding variable scope helps you manage data correctly in programs, like tracking sales or inventory in a shop system.

💼 Career

Many programming jobs require you to write functions that update shared data. Knowing variable scope prevents bugs and makes your code reliable.

1

Create initial sales variables

Create a variable called $totalSales and set it to 0. Then create a variable called $newSale and set it to 150.

PHP

$totalSales = 0;
$newSale = 150;
# Your code here

Hint

Use = to assign values to variables. Remember to end each line with a semicolon.

2

Write the addSale function

Write a function called addSale that takes one parameter $amount. Inside the function, use the global keyword to access $totalSales and add $amount to it.

PHP

$totalSales = 0;
$newSale = 150;

function addSale($amount) {
    # Your code here
}

Hint

Use global $totalSales; inside the function to access the variable outside.

3

Call the addSale function

Call the function addSale with the variable $newSale as the argument.

PHP

$totalSales = 0;
$newSale = 150;

function addSale($amount) {
    global $totalSales;
    $totalSales += $amount;
}

# Your code here

Hint

Call the function by writing its name and passing $newSale inside parentheses.

4

Print the total sales

Print the value of $totalSales using echo.

PHP

$totalSales = 0;
$newSale = 150;

function addSale($amount) {
    global $totalSales;
    $totalSales += $amount;
}

addSale($newSale);

# Your code here

Hint

Use echo $totalSales; to show the total sales amount.

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