Indexed array creation in PHP

Introduction

We use indexed arrays to store lists of items in order. Each item has a number called an index, starting from zero.

When you want to keep a list of names, like a guest list for a party.

When you need to store daily temperatures for a week.

When you want to keep track of scores in a game.

When you want to loop through a list of items one by one.

Syntax

PHP

<?php
// Create an indexed array
$array = array('value1', 'value2', 'value3');

// Or using short syntax
$array = ['value1', 'value2', 'value3'];
?>

Indexed arrays start with index 0 for the first item.

You can use either the array() function or the short [] syntax to create arrays.

Examples

This creates an empty indexed array with no items.

PHP

<?php
// Empty indexed array
$emptyArray = array();
?>

This array has one item at index 0.

PHP

<?php
// Array with one item
$singleItemArray = ["apple"];
?>

This array has three items with indexes 0, 1, and 2.

PHP

<?php
// Array with multiple items
$fruits = ["apple", "banana", "cherry"];
?>

Indexed arrays can hold different types of values together.

PHP

<?php
// Mixing types in an indexed array
$mixedArray = [10, "hello", 3.14];
?>

Sample Program

This program creates an indexed array of colors, prints it, adds a new color, then prints the updated array.

PHP

<?php
// Create an indexed array of colors
$colors = ["red", "green", "blue"];

// Print the array before adding a new color
print_r($colors);

// Add a new color at the end
$colors[] = "yellow";

// Print the array after adding
print_r($colors);
?>

Important Notes

Creating an indexed array is very fast, with time complexity O(1) for adding items at the end.

Indexed arrays use memory proportional to the number of items stored.

A common mistake is to confuse indexed arrays with associative arrays, which use named keys instead of numbers.

Use indexed arrays when order matters and you want to access items by their position number.

Summary

Indexed arrays store items in order, starting at index 0.

You can create them using array() or [] syntax.

They are useful for lists where position matters.

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