Modifying Elements by Index

Part of the Fundamentals section of Coddy's PHP journey — lesson 37 of 71.

You've learned how to access array elements by their index. Now let's see how to change those elements. Modifying an array element uses the same square bracket syntax, but with an assignment.

<?php
$fruits = ["Apple", "Banana", "Cherry"];

$fruits[1] = "Blueberry";

echo $fruits[1]; // Blueberry
?>

Here, we replaced "Banana" at index 1 with "Blueberry". The original value is gone—arrays don't keep a history of changes.

You can modify any element as long as you know its index:

<?php
$scores = [85, 90, 78];

$scores[0] = 95;  // Update first score
$scores[2] = 82;  // Update last score

echo $scores[0]; // 95
echo $scores[2]; // 82
?>

This is useful when you need to update data in your list—like correcting a typo, updating a price, or changing a user's status. The index tells PHP exactly which element to replace, leaving all other elements untouched.

Challenge

Easy

Read a line of input containing comma-separated values representing a list of colors (e.g., Red,Green,Blue,Yellow).

Then read three more inputs:

An integer index1 representing the first index to modify
A string newValue1 representing the new value for that index
An integer index2 representing the second index to modify

Create an array from the comma-separated input, then:

Modify the element at index1 to be newValue1
Modify the element at index2 to be Purple

Print the modified array elements on separate lines, in order from index 0 to the last index.

Example:

If the inputs are Red,Green,Blue,Yellow, 0, Orange, and 2, the output should be:

Orange
Green
Purple
Yellow

If the inputs are Apple,Banana,Cherry,Mango,Kiwi, 1, Grape, and 4, the output should be:

Apple
Grape
Cherry
Mango
Purple

Cheat sheet

To modify an array element, use the index with square brackets and assignment:

<?php
$fruits = ["Apple", "Banana", "Cherry"];

$fruits[1] = "Blueberry";  // Changes "Banana" to "Blueberry"

echo $fruits[1]; // Blueberry
?>

You can modify multiple elements by specifying different indices:

<?php
$scores = [85, 90, 78];

$scores[0] = 95;  // Update first element
$scores[2] = 82;  // Update last element
?>

The original value is replaced and not preserved. Other elements in the array remain unchanged.

Try it yourself

<?php
// Read the comma-separated colors
$colorsInput = trim(fgets(STDIN));
$colors = explode(',', $colorsInput);

// Read the modification inputs
$index1 = intval(trim(fgets(STDIN)));
$newValue1 = trim(fgets(STDIN));
$index2 = intval(trim(fgets(STDIN)));

// TODO: Write your code here
// 1. Modify the element at index1 to be newValue1
// 2. Modify the element at index2 to be "Purple"

// Output each element on a separate line
foreach ($colors as $color) {
    echo $color . "\n";
}
?>

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

Modifying Elements by Index

Cheat sheet

All lessons in Fundamentals