Indexed array creation in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code creating an indexed array?

Consider the following PHP code that creates an indexed array. What will be the output when it is run?

PHP

<?php
$array = array('apple', 'banana', 'cherry');
print_r($array);
?>

A Array ( apple, banana, cherry )

B Array ( [0] => apple [1] => banana [2] => cherry )

C Array ( [0] => apple [2] => banana [4] => cherry )

D Array ( [1] => apple [2] => banana [3] => cherry )

💡 Hint

Remember that indexed arrays in PHP start with index 0 by default.

In PHP, when you create an indexed array without specifying keys, the indexes start at 0 and increase by 1 for each element. So the keys are 0, 1, and 2 for the three elements.

❓ Predict Output

intermediate

What is the output of this PHP code using short array syntax?

Look at this PHP code that uses the short array syntax. What will it output?

PHP

<?php
$fruits = ['orange', 'grape', 'melon'];
var_dump($fruits);
?>

A array(3) { [0]=> string(6) "orange" [1]=> string(5) "grape" [2]=> string(5) "melon" }

B Array ( [1] => orange [2] => grape [3] => melon )

C array(3) { [1]=> string(6) "orange" [2]=> string(5) "grape" [3]=> string(5) "melon" }

D Array ( orange, grape, melon )

💡 Hint

var_dump shows detailed info including indexes starting at zero.

The short array syntax [] creates an indexed array starting at 0. var_dump shows the type, length, and keys with values. So keys are 0,1,2 with corresponding strings.

❓ Predict Output

advanced

What is the output of this PHP code mixing keys and values in an indexed array?

What will this PHP code output when run?

PHP

<?php
$array = array(0 => 'zero', 2 => 'two', 'one');
print_r($array);
?>

A Array ( [0] => zero [1] => one [2] => two )

B Array ( [0] => zero [1] => two [2] => one )

C Array ( [0] => zero [2] => two [3] => one )

D Array ( [0] => zero [2] => two [1] => one )

💡 Hint

When mixing explicit keys and implicit values, PHP assigns the next index after the highest numeric key.

The array has keys 0 and 2 explicitly. The next value 'one' has no key, so PHP assigns it key 3 (one more than highest key 2).

❓ Predict Output

advanced

What error or output does this PHP code produce?

Examine this PHP code snippet. What will happen when it runs?

PHP

<?php
$array = array(1 => 'a', 3 => 'b', 2 => 'c');
print_r($array);
?>

A Array ( [1] => a [3] => b [2] => c )

B Array ( [0] => a [1] => b [2] => c )

C SyntaxError: Unexpected token

D Array ( [1] => a [2] => c [3] => b )

💡 Hint

PHP arrays can have keys in any order; print_r shows them in insertion order.

The array keys are explicitly set as 1, 3, and 2. PHP keeps keys as given. print_r outputs them in the order inserted.

🧠 Conceptual

expert

How many elements are in this PHP indexed array after execution?

After running this PHP code, how many elements does the array contain?

PHP

<?php
$array = [];
$array[] = 'first';
$array[5] = 'sixth';
$array[] = 'seventh';
?>

A 2

B 5

C 4

D 3

💡 Hint

Appending without key uses the highest existing numeric key plus one.

Initially empty array. First append adds element at index 0. Then index 5 is set. Next append adds element at index 6 (5 + 1). So total elements: 3.

Practice

1. Which of the following correctly creates an indexed array with three elements in PHP?

easy

A. $arr = ["apple", "banana", "cherry"];

B. $arr = {"apple", "banana", "cherry"};

C. $arr = ("apple", "banana", "cherry");

D. $arr = array:"apple", "banana", "cherry";

Solution

1. Step 1: Recognize PHP array syntax

   PHP indexed arrays can be created using square brackets [] or the array() function.

2. Step 2: Check each option's syntax

   $arr = ["apple", "banana", "cherry"]; uses [] with comma-separated values, which is correct. Options A, B, and C use invalid syntax for arrays.

3. Final Answer:

   $arr = ["apple", "banana", "cherry"]; -> Option A

4. Quick Check:

   Correct array syntax = $arr = ["apple", "banana", "cherry"]; [OK]

Hint: Use square brackets [] or array() to create indexed arrays [OK]

Common Mistakes:

• Using curly braces {} instead of []
• Using parentheses () without array()
• Incorrect use of colons or other symbols

2. Which of the following is the correct syntax to create an indexed array with the elements 10, 20, and 30 in PHP?

easy

A. $numbers = [10; 20; 30];

B. $numbers = array(10, 20, 30);

C. $numbers = (10, 20, 30);

D. $numbers = {10, 20, 30};

Solution

1. Step 1: Recall PHP array creation syntax

   PHP allows creating arrays using array() with parentheses and comma-separated values.

2. Step 2: Validate each option

   $numbers = array(10, 20, 30); uses array() correctly. Options B, C, and D use invalid separators or brackets.

3. Final Answer:

   $numbers = array(10, 20, 30); -> Option B

4. Quick Check:

   array() with commas = $numbers = array(10, 20, 30); [OK]

Hint: Use commas inside array() or [] to separate elements [OK]

Common Mistakes:

• Using semicolons instead of commas
• Using parentheses without array()
• Using curly braces for arrays

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

$fruits = ["apple", "banana", "cherry"];
echo $fruits[1];

medium

A. banana

B. apple

C. cherry

D. Error

Solution

1. Step 1: Understand array indexing

   Indexed arrays start at index 0, so $fruits[0] = "apple", $fruits[1] = "banana".

2. Step 2: Identify the echoed element

   The code echoes $fruits[1], which is "banana".

3. Final Answer:

   banana -> Option A

4. Quick Check:

   Index 1 element = banana [OK]

Hint: Remember PHP arrays start at index 0 [OK]

Common Mistakes:

• Confusing index 1 with index 0
• Expecting output of entire array
• Syntax errors from missing semicolons

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

$colors = array["red", "green", "blue"];

medium

A. Array elements must be integers

B. Missing semicolon at the end

C. Using double quotes instead of single quotes

D. Using square brackets [] instead of parentheses () with array

Solution

1. Step 1: Check array() function syntax

   The array() function requires parentheses (), not square brackets [].

2. Step 2: Identify the syntax error

   The code uses array[ ... ] which is invalid syntax and causes an error.

3. Final Answer:

   Using square brackets [] instead of parentheses () with array -> Option D

4. Quick Check:

   array() needs () not [] [OK]

Hint: Use parentheses () with array(), not square brackets [] [OK]

Common Mistakes:

• Confusing array() with [] syntax
• Forgetting semicolon (though present here)
• Thinking quotes type matters for array creation

5. You want to create an indexed array of numbers from 1 to 5 in PHP without manually listing each number. Which code correctly does this?

hard

A. $numbers = array(1 to 5);

B. $numbers = [1..5];

C. $numbers = range(1, 5);

D. $numbers = {1, 2, 3, 4, 5};

Solution

1. Step 1: Recall PHP function for range creation

   PHP provides the range() function to create arrays with sequences of numbers.

2. Step 2: Evaluate each option

   $numbers = range(1, 5); uses range(1, 5) correctly. Options A, B, and D use invalid syntax or unsupported constructs.

3. Final Answer:

   $numbers = range(1, 5); -> Option C

4. Quick Check:

   Use range() for sequences [OK]

Hint: Use range(start, end) to create number arrays quickly [OK]

Common Mistakes:

• Using invalid range syntax like [1..5]
• Trying to write '1 to 5' inside array()
• Using curly braces {} for arrays