Question

Perform the following tasks for an array called table: a) Declare and create the array as an integer array that has three rows and three columns. Assume that the constant ARRAY_SIZE has been declared to be 3 . b) How many elements does the array contain? c) Use a for statement to initialize each element of the array to the sum of its indices. Assume that the integer variables \(x\) and \(y\) are declared as control variables.

Short answer

The array contains 9 elements, and each element is initialized with the sum of its indices.

Step-by-step solution

Declaring the Array

First, declare and create a 3x3 integer array called 'table'. Assume ARRAY_SIZE is 3. In most programming languages, this looks like: ```java int[][] table = new int[ARRAY_SIZE][ARRAY_SIZE]; // Java Example ``` This sets up the structure for our array.

Calculate Total Elements

To find out how many elements the array contains, multiply the number of rows by the number of columns. Since it's a 3x3 array:\[\text{Total Elements} = 3 \times 3 = 9\]So, the array contains 9 elements.

Initialize Array Elements

Next, use nested for loops to iterate through each element of the array and initialize each to the sum of its indices:```javafor (int x = 0; x < ARRAY_SIZE; x++) { for (int y = 0; y < ARRAY_SIZE; y++) { table[x][y] = x + y; }}```Here, each element at position \((x, y)\) in 'table' is set to the value of \(x + y\).

Key concepts

Array Declaration

In Java, when you want to work with a collection of similar data types, arrays come in handy. Declaring an array is like setting the stage for storing multiple values. For the given problem, you need to declare a two-dimensional array called 'table'. In Java, the declaration of this array is done with:
int[][] table;
This line tells the Java compiler that 'table' will be a 2D array. To create a 3x3 array, you'd typically assign it as follows:
table = new int[3][3];
Here, '3' indicates both the number of rows and columns. Java arrays use square brackets to define the dimensions. Initially, without assigning any values, the array elements default to zero since they're of type int.

Array Initialization

Once an array is declared, it’s essential to initialize it with values. Initialization gives each element of the array a definite value. In Java, you can do this during declaration or separately after declaration.
In this exercise, we use a nested loop structure to assign values to each element. The goal is to set each element to the sum of its indices. This involves looping over each index, pulling its "x" and "y" coordinates, and applying the given formula. Here's how you can do it:
for (int x = 0; x < ARRAY_SIZE; x++) {
for (int y = 0; y < ARRAY_SIZE; y++) {
table[x][y] = x + y;
}
}
In this code snippet, ARRAY_SIZE is 3, allowing iteration across all indices from 0 to 2 (both included). This ensures each element in the 'table' array gets initialized.

Nested Loops

Nested loops are an essential concept for multi-dimensional arrays, which allow you to iterate over complex data structures. Think of a nested loop as a loop within another loop. In this exercise, we use two for loops to traverse the 2D array 'table'.
The outer loop iterates through each row, while the inner loop goes through each column within that row. This ensures that every element in the rows and columns is accessed:

• The outer loop uses int x to control the iteration over the rows.
• The inner loop uses int y to iterate through each column of the current row.

This approach ensures that you visit each element at position (x, y) and allows for easy initialization or manipulation of array elements.

Indexing in Arrays

Understanding array indexing is fundamental when working with arrays. Indexing refers to accessing each element within the array via an index number. For a 2D array like 'table', indexing is done using two indices, one for the row and one for the column.
In Java, array indexing starts at 0. Therefore, in an array with a size of 3, valid indices range from 0 to 2. The element in the first row and first column is accessed with table[0][0]. As a result, the last element in a 3x3 array is accessible via table[2][2].
This 0-based indexing is crucial for correctly looping through arrays, preventing common errors like ArrayIndexOutOfBounds exceptions. It’s also important to remember this while performing operations like initialization or retrieval of values from the arrays.