Question

What is the output of the following C++ code? int *myList = new int[5]; int *yourList = new int[10]; myList[0] = 3; for (int i = 1; i < 5; i++) myList[i] = myList[i - 1] + i; for (int i = 0; i < 5; i++) { yourList[i] = myList[i] + 4; yourList[i + 5] = myList[4 - i] - 3; } cout << "myList: "; for (int i = 0; i < 5; i++) cout << myList[i] << " "; cout << endl; cout << "yourList: "; for (int i = 0; i < 10; i++) cout << yourList[i] << " "; cout << endl;

Short answer

myList: 3 4 6 9 13; yourList: 7 8 10 13 17 10 6 3 1 0.

Step-by-step solution

Initialize Arrays and Set Initial Value

Two arrays, `myList` and `yourList`, are declared using dynamic memory allocation. `myList` has 5 elements, while `yourList` has 10 elements. The initial entry for `myList` is set to `3`. Code: `myList[0] = 3;`

Fill 'myList' Using a Loop

A `for` loop fills each element of `myList` starting from index 1, where each element is the sum of the previous element and the current index value. Loop: `for (int i = 1; i < 5; i++) myList[i] = myList[i - 1] + i;` Result after loop: - myList[0] = 3 - myList[1] = 3 + 1 = 4 - myList[2] = 4 + 2 = 6 - myList[3] = 6 + 3 = 9 - myList[4] = 9 + 4 = 13

Populate 'yourList' Using Two Conditions

Two conditions are used to fill `yourList`. The array is populated in two parts: - First part: Each element from 0 to 4 of `yourList` is the element at the same index in `myList` plus 4. - Second part: Each element from 5 to 9 of `yourList` is the element at an index in `myList` starting from the last element minus 3. Loop Code: - `yourList[i] = myList[i] + 4;` - `yourList[i + 5] = myList[4 - i] - 3;` Outcome: - yourList[0] = 3 + 4 = 7 - yourList[1] = 4 + 4 = 8 - yourList[2] = 6 + 4 = 10 - yourList[3] = 9 + 4 = 13 - yourList[4] = 13 + 4 = 17 - yourList[5] = 13 - 3 = 10 - yourList[6] = 9 - 3 = 6 - yourList[7] = 6 - 3 = 3 - yourList[8] = 4 - 3 = 1 - yourList[9] = 3 - 3 = 0

Output the Results

Finally, the program prints out the values of `myList` and `yourList`. Output Code: - Printing `myList`: Outputs `3 4 6 9 13` - Printing `yourList`: Outputs `7 8 10 13 17 10 6 3 1 0`

Key concepts

Arrays in C++

In C++, arrays are a powerful tool for storing data. They allow you to hold multiple values of the same type under one variable name and access each through an index. In our code example, two arrays are created using dynamic memory allocation: `myList` and `yourList`. This offers flexibility as the exact size of an array can be set at runtime. However, remember that arrays in C++ always start indexing from zero.

Key points about arrays:

• Initialization: Declare arrays using the `new` keyword to allocate memory dynamically, like `int *myList = new int[5];`.
• Accessing Elements: Access any element using the index inside square brackets, such as `myList[0]` for the first element.
• Modifying Elements: Modify elements by directly assigning a value to the indexed position, e.g., `myList[0] = 3;` sets the first element to 3.
• Dynamic Memory: Remember to deallocate dynamic memory using `delete[]` when done to prevent memory leaks.

Understanding arrays is crucial for efficiently handling multiple data points in C++ programs.

Loops in Programming

Loops are essential structures that allow the repetition of code until a specific condition is met. They help automate repetitive tasks, saving time and reducing errors. In our exercise, loops are used to populate and manipulate the `myList` and `yourList` arrays seamlessly.

Some important loop concepts:

• For Loop: Ideal when the number of iterations is known. It has three main parts - a starting point, a condition, and an increment/decrement. For example, `for (int i = 1; i < 5; i++)` starts with `i` at 1, loops until `i` is less than 5, and increases `i` by one each time.
• Iterative Operations: Within each iteration, operations like addition can be performed on array items. For instance, `myList[i] = myList[i - 1] + i;` increments each element based on its predecessors.
• Nesting Loops: Often you will want to nest loops for more complex actions, though our code doesn't require nested loops, it's a common pattern.

Loops are powerful, but must be used with care to avoid infinite loops or errors from exceeding array bounds.

Pointer Arithmetic

Pointers in C++ are variables that store the memory address of another variable. Pointer arithmetic involves operations that manipulate these addresses, especially useful when dealing with arrays since array names often act as pointers to their first element.

Basics of pointer arithmetic:

• Access by Address: By using pointers, you can directly access and manipulate data in memory.
• Moving Through Arrays: By incrementing a pointer, you can advance to the next element in an array because array memory is contiguous. For instance, if `p` is a pointer to an element in `myList`, `p++` moves it to the next element.
• Dynamic Memory: Since arrays like `myList` are dynamicaly allocated, they naturally work with pointer arithmetic, enabling efficient data manipulation.
• Operations: You can perform arithmetic on pointers using `+`, `-`, `++`, and `--`. These operations respect data type sizes, moving the pointer by the size of the data type it points to.

Pointer arithmetic can be complex and error-prone, so understanding the size of data types and how pointers reference memory is critical.