Associative array creation in PHP - Mini Project: Build & Apply

Associative Array Creation in PHP

📖 Scenario: You are creating a small contact list for your friends. Each friend has a name and a phone number.

🎯 Goal: Build an associative array in PHP that stores friends' names as keys and their phone numbers as values.

📋 What You'll Learn

Create an associative array called contacts with exact key-value pairs

Add a variable called new_contact set to 'Bob'

Use the array_key_exists function to check if a contact exists

Print the phone number of the new_contact if it exists

💡 Why This Matters

🌍 Real World

Associative arrays are used to store data with named keys, like contact lists, settings, or user profiles.

💼 Career

Knowing how to create and use associative arrays is essential for backend web development and data handling in PHP.

1

Create the contacts associative array

Create an associative array called contacts with these exact entries: 'Alice' => '123-4567', 'Bob' => '234-5678', and 'Charlie' => '345-6789'.

PHP

<?php

// Create the associative array 'contacts' with the given entries
// Your code here

Hint

Use square brackets [] to create the array and separate key-value pairs with =>.

2

Add a new_contact variable

Add a variable called new_contact and set it to the string 'Bob'.

PHP

 '123-4567',
    'Bob' => '234-5678',
    'Charlie' => '345-6789'
];

// Add the variable 'new_contact' with value 'Bob'
// Your code here

Hint

Use = to assign the string 'Bob' to the variable new_contact.

3

Check if new_contact exists in contacts

Use an if statement with array_key_exists to check if new_contact is a key in contacts. Inside the if, assign the phone number to a variable called phone_number.

PHP

 '123-4567',
    'Bob' => '234-5678',
    'Charlie' => '345-6789'
];

$new_contact = 'Bob';

// Use if and array_key_exists to check if 'new_contact' is in 'contacts'
// If yes, assign the phone number to 'phone_number'
// Your code here

Hint

Use array_key_exists($new_contact, $contacts) inside the if condition.

4

Print the phone number

Print the value of phone_number using echo.

PHP

 '123-4567',
    'Bob' => '234-5678',
    'Charlie' => '345-6789'
];

$new_contact = 'Bob';

if (array_key_exists($new_contact, $contacts)) {
    $phone_number = $contacts[$new_contact];
}

// Print the phone number
// Your code here

Hint

Use echo $phone_number; to display the phone number.

Practice

1. Which of the following is the correct way to create an associative array in PHP with keys "name" and "age"?

easy

A. $person = ("name" => "Alice", "age" => 30);

B. $person = {"name": "Alice", "age": 30};

C. $person = array("Alice", 30);

D. $person = ["name" => "Alice", "age" => 30];

Solution

1. Step 1: Understand PHP associative array syntax

   Associative arrays use square brackets with key => value pairs.

2. Step 2: Identify correct syntax among options

   $person = ["name" => "Alice", "age" => 30]; uses square brackets and => correctly; others use invalid syntax.

3. Final Answer:

   $person = ["name" => "Alice", "age" => 30]; -> Option D

4. Quick Check:

   Associative array = key => value pairs [OK]

Hint: Use square brackets and => for associative arrays [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Using colon (:) instead of =>
• Creating indexed arrays instead of associative

2. Which of the following PHP code snippets will cause a syntax error when creating an associative array?

easy

A. $data = ["key1" : "value1", "key2" : "value2"];

B. $data = array("key1" => "value1", "key2" => "value2");

C. $data = ["key1" => "value1", "key2" => "value2"];

D. $data = ['key1' => 'value1', 'key2' => 'value2'];

Solution

1. Step 1: Check the syntax for key-value pairs

   PHP uses => to assign values to keys, not colon (:).

2. Step 2: Identify the invalid syntax

   $data = ["key1" : "value1", "key2" : "value2"]; uses colon (:) which is invalid in PHP associative arrays.

3. Final Answer:

   $data = ["key1" : "value1", "key2" : "value2"]; -> Option A

4. Quick Check:

   Use => not : for keys in PHP arrays [OK]

Hint: Remember PHP uses =>, not : for associative arrays [OK]

Common Mistakes:

• Using colon (:) instead of =>
• Mixing array() and [] syntax incorrectly
• Missing commas between pairs

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

$arr = ["fruit" => "apple", "color" => "red"];
echo $arr["color"];

medium

A. red

B. color

C. apple

D. fruit

Solution

1. Step 1: Understand array key access

   Accessing $arr["color"] returns the value for key "color".

2. Step 2: Identify the value for key "color"

   Value is "red", so echo outputs "red".

3. Final Answer:

   red -> Option A

4. Quick Check:

   Key "color" = "red" [OK]

Hint: Access values by keys with $array["key"] [OK]

Common Mistakes:

• Confusing keys and values
• Using wrong quotes or missing quotes
• Trying to access with dot notation

4. Identify the error in the following PHP code that tries to create an associative array:

$info = ["name" => "John", "age" = 25];

medium

A. Missing comma between elements

B. Keys should not be in quotes

C. Using = instead of => for key-value pair

D. Array must use array() syntax

Solution

1. Step 1: Check key-value assignment syntax

   PHP requires => to assign values to keys, not =.

2. Step 2: Locate incorrect assignment

   "age" = 25 uses = instead of =>, causing syntax error.

3. Final Answer:

   Using = instead of => for key-value pair -> Option C

4. Quick Check:

   Use => for key-value pairs [OK]

Hint: Use =>, not =, between key and value [OK]

Common Mistakes:

• Using single = instead of =>
• Omitting commas between pairs
• Not quoting string keys

5. You want to create an associative array in PHP that maps product names to their prices, but only include products with a price greater than 20. Which code correctly creates this filtered associative array?

hard

A. $products = ["apple" => 15, "banana" => 25, "cherry" => 30];
$filtered = [];
foreach ($products as $name, $price) {
if ($price > 20) {
$filtered[$name] = $price;
}
}

B. $products = ["apple" => 15, "banana" => 25, "cherry" => 30];
$filtered = [];
foreach ($products as $name => $price) {
if ($price > 20) {
$filtered[$name] = $price;
}
}

C. $products = ["apple" => 15, "banana" => 25, "cherry" => 30];
$filtered = array_filter($products, function($name, $price) {
return $price > 20;
});

D. $products = ["apple" => 15, "banana" => 25, "cherry" => 30];
$filtered = [];
foreach ($products as $price => $name) {
if ($price > 20) {
$filtered[$name] = $price;
}
}

Solution

1. Step 1: Understand foreach key-value syntax

   Use foreach ($array as $key => $value) to access keys and values correctly.

2. Step 2: Filter products with price > 20

   $products = ["apple" => 15, "banana" => 25, "cherry" => 30]; $filtered = []; foreach ($products as $name => $price) { if ($price > 20) { $filtered[$name] = $price; } } correctly checks price and assigns filtered items to new array.

3. Final Answer:

   The code using foreach ($products as $name => $price) -> Option B

4. Quick Check:

   foreach ($arr as $key => $value) for associative arrays [OK]

Hint: Use foreach ($arr as $key => $value) to access associative arrays [OK]

Common Mistakes:

• Swapping key and value variables in foreach
• Using incorrect foreach syntax with two variables separated by comma
• Misusing array_filter with wrong callback parameters