Question

Perform the following tasks for an array called fractions: a) Declare a constant ARRAY_SIZE that's initialized to 10 b) Declare an array with ARRAY_SIZE elements of type double, and initialize the elements to 0. c) Refer to array element 4 d) Assign the value 1.667 to array element 9 e) Assign the value 3.333 to array element 6 f) Sum all the elements of the array, using a for statement. Declare the integer variable \(x\) as a control variable for the loop.

Short answer

Declare ARRAY_SIZE as 10, initialize an array of doubles with 10 elements to 0, reference the 5th element with fractions[4], assign 1.667 to fractions[9], assign 3.333 to fractions[6], and sum all elements of the array in a for loop using a control variable 'x'.

Step-by-step solution

Declare a constant for the array size

Start by defining a constant named ARRAY_SIZE and initialize it to 10. This constant will be used to specify the size of the array. In most programming languages, you can define a constant using a keyword like 'const'. The syntax will depend on the programming language in use.

Declare and initialize the array

Using the constant ARRAY_SIZE, declare an array of type double with ARRAY_SIZE elements. Initialize all elements to 0. The syntax for array declaration and initialization may vary slightly depending on the programming language, but it generally looks something like 'double fractions[ARRAY_SIZE] = {0};'

Refer to array element 4

To reference the 5th element in the array (element at index 4, since array indices usually start at 0), you simply use the array name followed by the index in square brackets: 'fractions[4]'.

Assign a value to array element 9

Assign the value 1.667 to the last element in the array, which is element 9 (10th element): 'fractions[9] = 1.667;'. Remember that array indices start at 0, so the 10th element is at index 9.

Assign a value to array element 6

Assign the value 3.333 to the 7th element of the array (element at index 6): 'fractions[6] = 3.333;'.

Sum all the elements of the array

To sum all elements of the array, use a for loop with a control variable named 'x'. Initialize 'x' to 0, and in each iteration, add the value of 'fractions[x]' to a sum variable. The loop will continue until 'x' is less than ARRAY_SIZE. The sum variable should be initialized to 0 before entering the loop.

Key concepts

Declaring Arrays

When starting out with Java programming, one of the first structures you'll encounter is the array, a fundamental data type used to store sequences of values. Declaring an array in Java begins with specifying the type of data that it will hold, followed by square brackets to indicate that you are creating an array, and then the array's name. For instance, if you want to store decimal numbers, which are represented as double in Java, your array declaration would look like this: double[] fractions;.

However, simply declaring an array does not actually create it or allocate any space in memory for its elements. For that, you would need to either initialize it immediately or assign it an array object at a later point in your code. But declaring an array is an essential first step, telling the Java compiler what type of data we plan to store and how we'll access that data.

Initializing Arrays

Initializing an array in Java provides the actual space to hold the data we intend to store. You can initialize an array in multiple ways, one of which is to create an array with pre-defined size and default values using the new keyword. For example, to initialize the fractions array with a size of ARRAY_SIZE and default values of 0, you would write: fractions = new double[ARRAY_SIZE]; Arrays in Java are zero-initialized, which means each element will automatically hold a zero value right after array creation.

If we combine the declaration with initialization, we could simplify these two actions into a single line of code like this: double[] fractions = new double[ARRAY_SIZE];. Initialization is a crucial step, as it is what actually allocates the memory for your array, allowing it to store the values you give it.

Array Indexing

Array indexing is how you access or modify the elements within an array. Java arrays are zero-indexed, meaning that the first element is accessed with an index of 0, the second element with an index of 1, and so on. If you wish to refer to the fifth element in the fractions array, you would use the index 4: double fifthElement = fractions[4];. Notably, trying to access an index that is outside the range of the array (for instance, fractions[10] when the array only has 10 elements) will result in an ArrayIndexOutOfBoundsException, a common error that signals that your program is attempting to read or write data outside the permitted bounds of the array.

To work within the array safely, always keep your indices within 0 and ARRAY_SIZE - 1. Understanding array indexing is crucial for manipulating array data effectively and avoiding errors in your programs.

For Loop in Java

The 'for' loop in Java is a control flow statement that allows you to execute a block of code multiple times, which is especially useful when working with arrays. To sum all elements of an array, you can use a 'for' loop to iterate through each element by its index. Starting with an initialization of your control variable (such as int x = 0;), you then set the loop's continuation condition (x < ARRAY_SIZE), and increment your control variable (x++) after each iteration of the loop. Inside the loop, you would add the current array element to a sum variable.

Here is what the for loop could look like when summing the elements of the fractions array:

double sum = 0;for (int x = 0; x < ARRAY_SIZE; x++) {    sum += fractions[x];}

Learning to use 'for' loops effectively will help you perform repetitive tasks with ease and is a cornerstone of array manipulation in Java.