Question

Consider the following declaration: int list[] = {3, 8, 10, 13, 6, 11}; a. Write a C++ code that will output the value stored in each component of list. b. Write a C++ code that will set the values of the first five components of list as follows: The value of the ith component is the value of the ith component minus three times the value of the (i+1)th component.

Short answer

A loop is used to print each element, then modify the first five components using a calculated formula.

Step-by-step solution

Iterate through the list

To output each value stored in the array `list`, use a `for` loop to iterate through its elements. C++ arrays use zero-based indexing, so the loop should run from 0 to 5.

Output list components

Within the loop, use `cout` to print each element of the array. The loop index variable, `i`, serves as the index to access each element.

Example code for part a

```cpp #include int main() { int list[] = {3, 8, 10, 13, 6, 11}; for(int i = 0; i < 6; i++) { std::cout << list[i] << std::endl; } return 0; } ``` This code will print all components of the `list` array from the first to the sixth component.

Modify components according to the new formula

To modify the first five components, again use a `for` loop that iterates for the first five indices. Reassign each element to be the current element minus three times the next element.

Prepare for out of range

During the iteration, for the calculation `list[i] - 3 * list[i+1]` ensure that `i+1` does not exceed the array bounds by limiting the loop to index 4. The loop should stop at the fifth element.

Example code for part b

```cpp #include int main() { int list[] = {3, 8, 10, 13, 6, 11}; for(int i = 0; i < 5; i++) { list[i] = list[i] - 3 * list[i+1]; } for(int i = 0; i < 6; i++) { std::cout << list[i] << std::endl; } return 0; } ``` This code will modify the first five components of the array and then print all components, showing the changes.

Key concepts

C++ For Loop

The `for` loop in C++ is a fundamental construct that allows us to execute a block of code repeatedly for a specified number of times. This is perfect for operating on arrays, as it lets us easily iterate over each element. A typical `for` loop structure includes initialization, a condition, and an increment/decrement statement.

In the given problem, the `for` loop is used to traverse the `list` array from the first to the last element. The loop is structured as `for(int i = 0; i < 6; i++)`, where:

• Initialization: `int i = 0` sets the starting point at index 0.
• Condition: `i < 6` continues the loop until `i` is equal to 6, covering the array's length.
• Increment: `i++` increases the index by 1 in each iteration.

This loop allows each element in the array `list` to be addressed at its respective index, showcasing the utility of `for` loops in array operations.

C++ cout

`cout` in C++ is a part of the input/output stream used to display output to the standard output, typically the console. It's used in conjunction with the stream insertion operator `<<` to direct output. In the code, we see `std::cout << list[i] << std::endl;` inside a `for` loop. This line does the following:

• Outputs the current element of the array `list[i]`.
• Uses `std::endl` to insert a newline character after each value, ensuring each number appears on a separate line.

Including `std::` before `cout` specifies that we are using a standard library function, which is important if we are working outside the `std` namespace or wish to be explicit.

C++ Indexing

Indexing in C++ arrays is how we access each element. C++ uses zero-based indexing, which means the first element is accessed with index 0, the second with index 1, and so on. In the exercise, the integer array `list[] = {3, 8, 10, 13, 6, 11};` holds six elements. To access or modify any element in the array, you use its index. For example, `list[0]` accesses the first element and `list[5]` accesses the last. When using loops:

• The loop index variable `i` serves as the array index.
• You must ensure that your loops respect the array's bounds to prevent accessing invalid memory locations. In this case, the loop runs from 0 to 5 to cover all six elements.

Proper understanding of indexing is crucial for both accessing and modifying array data.

Array Modification in C++

Modifying elements within a C++ array allows us to perform calculations or adjustments directly on the stored values. The exercise involves recalculating the first five elements of the `list` array by changing each to the result of `list[i] - 3 * list[i+1]`. To do this safely, consider:

• Using a for loop that iterates only until the second-to-last element (index 4), to prevent out-of-bounds errors with `list[i+1]`.
• Directly accessing and updating array elements using `list[i] = ...`.
• Recognizing that after modification, elements in the list will change, which affects further calculations if modified elements are used in subsequent iterations.

The process of array modification provides a dynamic way to utilize and update data stored in arrays, an essential aspect of many algorithm implementations.