Multidimensional arrays in PHP - Step-by-Step Execution

Concept Flow - Multidimensional arrays

Create outer array

↓

Add inner arrays as elements

↓

Access elements by multiple indexes

↓

Use nested loops to traverse

↓

Process or print each element

Start by creating an array that holds other arrays. Access elements using two or more indexes. Use nested loops to go through all elements.

Execution Sample

PHP

<?php
$matrix = [
  [1, 2],
  [3, 4]
];
echo $matrix[0][1];
?>

This code creates a 2x2 array and prints the element in the first row, second column.

Execution Table

Step	Action	Variable State	Output
1	Create outer array with two inner arrays	$matrix = [[1,2],[3,4]]
2	Access $matrix[0]	Returns [1, 2]
3	Access $matrix[0][1]	Returns 2
4	Print value 2		2
5	End of script

💡 Script ends after printing the element at $matrix[0][1]

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$matrix	undefined	[[1,2],[3,4]]	[[1,2],[3,4]]	[[1,2],[3,4]]	[[1,2],[3,4]]
$matrix[0]	undefined	undefined	[1,2]	[1,2]	[1,2]
$matrix[0][1]	undefined	undefined	undefined	2	2

Key Moments - 3 Insights

Why do we use two indexes like $matrix[0][1] to access elements?

Because $matrix is an array of arrays. The first index selects the inner array, the second index selects the element inside that inner array. See execution_table rows 2 and 3.

What happens if we try to access $matrix[2][0]?

Since $matrix has only two inner arrays (indexes 0 and 1), $matrix[2] does not exist. This will cause an error or undefined behavior. The execution_table shows valid indexes only.

How do nested loops help with multidimensional arrays?

Nested loops let us go through each inner array and then each element inside it, covering all elements. This is implied in the concept_flow step 'Use nested loops to traverse'.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of $matrix[0] at step 2?

A 2

B [1, 2]

C [3, 4]

D undefined

💡 Hint

Check the 'Variable State' column at step 2 in execution_table.

At which step does the code output the number 2?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Output' column in execution_table to find when '2' is printed.

If we add another inner array [5,6] to $matrix, how would the variable tracker change after step 1?

A $matrix would be [[1,2],[3,4],[5,6]]

B $matrix would be [[1,2],[3,4]] only

C $matrix would be [5,6]

D $matrix would be undefined

💡 Hint

Refer to the 'After Step 1' column in variable_tracker and imagine adding one more inner array.

Concept Snapshot

Multidimensional arrays are arrays inside arrays.
Access elements with multiple indexes like $array[row][col].
Use nested loops to visit all elements.
Useful for grids, tables, or matrices.
In PHP, arrays can hold arrays easily.
Remember indexes start at 0.

Full Transcript

This example shows how to create and use multidimensional arrays in PHP. We start by making an array that contains other arrays. Each inner array holds numbers. To get a number, we use two indexes: the first picks the inner array, the second picks the number inside it. The code prints the number 2 from the first inner array's second element. Variables keep their values until the script ends. Beginners often wonder why two indexes are needed or what happens if an index is missing. Nested loops help to go through all elements one by one. This is a simple way to handle tables or grids in code.