Question

What is stored in myList after the following C++ code executes? double myList[5]; myList[0] = 3.0; myList[1] = 4.0; for (int i = 2; i < 5; i++) { myList[i] = myList[i - 1] * myList[i - 2]; if (i > 3) myList[i] = myList[i] / 4; }

Short answer

myList stores [3.0, 4.0, 12.0, 48.0, 144.0].

Step-by-step solution

Initialize the Array Portion

The first two elements of the array `myList` are explicitly initialized. Hence, `myList[0] = 3.0` and `myList[1] = 4.0`.

Iterate and Calculate for Subsequent Elements

We enter the `for` loop where `i` ranges from 2 to 4. For each iteration, compute `myList[i]` using the formula `myList[i] = myList[i - 1] * myList[i - 2]`. For `i = 2`, the computation is:\[ myList[2] = myList[1] \times myList[0] = 4.0 \times 3.0 = 12.0 \]

Continuing the Iteration

Next, for `i = 3`, evaluate:\[ myList[3] = myList[2] \times myList[1] = 12.0 \times 4.0 = 48.0 \]

Applying Condition and Completing the Loop

For `i = 4`, perform the multiplication first:\[ myList[4] = myList[3] \times myList[2] = 48.0 \times 12.0 = 576.0 \]Since `i > 3`, divide the result by 4:\[ myList[4] = \frac{576.0}{4} = 144.0 \]

Key concepts

C++ Programming

C++ is a powerful programming language that offers a combination of high-level programming features and low-level capabilities. Understanding C++ can often start with learning about arrays and loops, as they are fundamental concepts used in everyday programming tasks. C++ allows for direct manipulation of memory with pointers and provides rich libraries that make complex operations more manageable. It supports procedural, object-oriented, and generic programming styles.

Key features of C++ include its syntax, which is similar to that of its predecessor C. It also provides tools for data abstraction, encapsulation, and polymorphism. Whether you're working on a complex system or a simple program, C++ gives you the flexibility to manage resources and control operations closely.

Control Structures

Control structures in C++ are used to direct the flow of a program's execution. They are essential in making decisions and iterating over data.

In the context of the exercise, we utilize a for loop, which is a type of control structure. The `for` loop simplifies iteration by allowing programmers to specify initialization, condition checking, and increment all in one line. Here, it controls how many times we execute a block of code to fill our array.

Within the loop, we also have an if statement. The if statement is a conditional control structure that executes a specific block of code when a condition is true. In our code, this condition checks whether the index `i` is greater than 3, providing logic that alters the stored values based on the index position.

Array Initialization

In C++, an array is initialized by declaring the type and size. Once an array is declared, its elements can be directly assigned values.

For our exercise, we declare an array named `myList` of type `double` with 5 elements. This tells the compiler to allocate memory for 5 double values. Each element in the array can store a double value independently, and elements can be accessed by their index position.

We started by assigning values to the first two elements explicitly: `myList[0] = 3.0;` and `myList[1] = 4.0;`. This process is called explicit initialization. It's important to remember that since arrays use zero-based indexing in C++, the index of the first element is 0.

Iteration in Arrays

Iteration is the process of executing a set of instructions repeatedly. When working with arrays in C++, iteration is often necessary to perform operations on all elements.

In our example, a `for` loop iterates through the array, starting from index 2 up to 4, to compute the values of subsequent elements. The loop relies on the values of previous elements to calculate the next ones. Specifically, it uses the operations `myList[i] = myList[i - 1] * myList[i - 2]` inside the loop block.

The iteration is efficient since it not only calculates values consecutively but also includes conditional logic to modify these values based on given criteria, like dividing the result by 4 if the index is greater than 3. This shows how iteration can not only process data but also include logic for data transformation as needed.