A two-dimensional array, as represented in pseudocode, is defined as a collection of items organized into rows and columns.

In essence, a two-dimensional array can be thought of as an array of arrays. This data structure stores data in a tabular format, which is particularly beneficial for organizing information in a way that is easy to visualize or manipulate, such as within a matrix or grid.

To define a two-dimensional array in pseudocode, you first declare the array and then specify its dimensions. For example, you might write, “Declare an array $A[5][5]$” to create a $5 \times 5$ array. This declaration indicates that array $A$ consists of $5$ rows and $5$ columns, allowing it to hold a total of $25$ elements. For additional information on how data types influence array structures, please refer to our notes on the topic.

Each element within the array can be accessed using its row index and column index. For instance, $A[2][3]$ refers to the element located in the third row and fourth column of the array. It’s crucial to remember that in most programming languages, array indices start at $0$, not $1$. Therefore, the first element in the array is accessed with $A[0][0]$, rather than $A[1][1]$. To gain further insight into the functioning of two-dimensional arrays, check out our dedicated section.

When working with two-dimensional arrays in pseudocode, nested loops are commonly employed to traverse the array and perform operations on each element. The outer loop typically iterates over the rows, while the inner loop iterates over the columns. For example, you might write a loop like “For $i = 0$ to $4$” and then within that loop, include another loop like “For $j = 0$ to $4$” to access each element in a $5 \times 5$ array. For a comprehensive understanding of algorithms applicable to these structures, please visit our guide on the subject.

Summary for IB Computer Science Tutors: A two-dimensional array is a structured collection of items arranged in rows and columns, resembling a table. You can define it in pseudocode by declaring its dimensions, such as “Declare an array $A[5][5]$” for a $5 \times 5$ grid. Access specific elements using row and column indices, noting that counting begins at $0$. To traverse the entire array, nested loops are utilized.