Array access and modification in PHP - Mini Project: Build & Apply

Array access and modification

📖 Scenario: You are managing a small fruit store inventory. You have a list of fruits and their quantities. You want to update the quantities as fruits are sold or restocked.

🎯 Goal: Learn how to access and modify values in an array in PHP by updating fruit quantities.

📋 What You'll Learn

Create an associative array with fruit names as keys and quantities as values

Create a variable to hold the quantity to add or subtract

Modify the quantity of a specific fruit in the array

Print the updated array

💡 Why This Matters

🌍 Real World

Managing inventory in a store requires updating quantities as items are sold or restocked.

💼 Career

Knowing how to access and modify arrays is essential for backend development and data management.

1

Create the initial fruit inventory array

Create an associative array called fruits with these exact entries: 'apple' => 10, 'banana' => 5, 'orange' => 8.

PHP

# Create the 'fruits' array with the given entries
# Your code here

Hint

Use square brackets [] to create an associative array with keys and values.

2

Create a variable for quantity change

Create a variable called change and set it to -3 to represent selling 3 fruits.

PHP

 10, 'banana' => 5, 'orange' => 8];
# Create the 'change' variable and set it to -3
# Your code here

Hint

Use the = sign to assign the value -3 to the variable change.

3

Modify the quantity of bananas

Update the quantity of banana in the fruits array by adding the value of change to it.

PHP

 10, 'banana' => 5, 'orange' => 8];
$change = -3;
# Update the quantity of 'banana' by adding 'change'
# Your code here

Hint

Use $fruits['banana'] += $change; to add change to the current banana quantity.

4

Print the updated fruits array

Use print_r to display the updated fruits array.

PHP

 10, 'banana' => 5, 'orange' => 8];
$change = -3;
$fruits['banana'] += $change;
# Print the 'fruits' array
# Your code here

Hint

Use print_r($fruits); to print the array in a readable format.

Practice

1. What is the correct way to access the first element of an array $arr in PHP?

easy

A. $arr{0}

B. $arr[1]

C. $arr[0]

D. $arr->0

Solution

1. Step 1: Understand PHP array indexing

   PHP arrays start at index 0, so the first element is at index 0.

2. Step 2: Identify correct syntax for array access

   Use square brackets with the index number: $arr[0].

3. Final Answer:

   $arr[0] -> Option C

4. Quick Check:

   First element index = 0 [OK]

Hint: First element is always at index 0 in PHP arrays [OK]

Common Mistakes:

• Using index 1 for first element
• Using curly braces for array access
• Using object property syntax

2. Which of the following is the correct way to change the value of the third element in array $arr to 10?

easy

A. $arr(3) = 10;

B. $arr[2] = 10;

C. $arr->2 = 10;

D. $arr{3} = 10;

Solution

1. Step 1: Identify the index of the third element

   Arrays start at 0, so the third element is at index 2.

2. Step 2: Use correct syntax to assign value

   Use square brackets with index 2: $arr[2] = 10;.

3. Final Answer:

   $arr[2] = 10; -> Option B

4. Quick Check:

   Index 2 for third element assignment [OK]

Hint: Use square brackets and zero-based index to modify array [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Using object property syntax
• Using wrong index number

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

$arr = [5, 10, 15];
$arr[1] = $arr[1] + 5;
echo $arr[1];

medium

A. 15

B. 10

C. 20

D. 5

Solution

1. Step 1: Understand initial array values

   $arr = [5, 10, 15]; so $arr[1] is 10.

2. Step 2: Calculate new value of $arr[1]

   $arr[1] = $arr[1] + 5 means 10 + 5 = 15.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   10 + 5 = 15 [OK]

Hint: Add to existing value using $arr[index] + number [OK]

Common Mistakes:

• Printing old value without update
• Adding index instead of value
• Confusing array indexes

4. Identify the error in the following PHP code snippet:

$arr = [1, 2, 3];
$arr[3] = 4;
echo $arr[3];

medium

A. Accessing an undefined index causes an error

B. Cannot echo array elements directly

C. Syntax error in array declaration

D. Assigning to index 3 adds a new element without error

Solution

1. Step 1: Check array indexes and assignment

   Array has indexes 0,1,2 initially. Assigning $arr[3] = 4 adds a new element at index 3.

2. Step 2: Confirm if this causes error

   PHP allows adding new elements by assigning to new indexes without error.

3. Final Answer:

   Assigning to index 3 adds a new element without error -> Option D

4. Quick Check:

   PHP arrays auto-expand on new index assignment [OK]

Hint: Assigning new index adds element; no error in PHP [OK]

Common Mistakes:

• Thinking accessing undefined index causes error
• Confusing syntax error with runtime behavior
• Believing echo can't print array elements

5. Given the array $arr = [2, 4, 6, 8];, which code snippet correctly doubles each element's value by modifying the array in place?

hard

A. for ($i = 0; $i < count($arr); $i++) { $arr[$i] *= 2; }

B. $arr = array_fill(0, count($arr), 2 * $arr[0]);

C. array_map(fn($v) => $v * 2, $arr);

D. foreach ($arr as $value) { $value = $value * 2; }

Solution

1. Step 1: Understand how to modify array elements in place

   Using a for loop with index allows direct modification of each element.

2. Step 2: Analyze each option

   A: foreach copies values, does not modify original array.
   B: array_fill replaces all elements with same value, incorrect.
   C: array_map returns new array, original unchanged.
   D: for loop modifies $arr[$i] directly.

3. Final Answer:

   for ($i = 0; $i < count($arr); $i++) { $arr[$i] *= 2; } -> Option A

4. Quick Check:

   Use indexed loop to modify array elements [OK]

Hint: Use for loop with indexes to change array elements directly [OK]

Common Mistakes:

• Modifying foreach loop variable instead of array
• Expecting array_map to change original array
• Using array_fill incorrectly