Question

include using namespace std; int main() { int count; int alpha[5]; alpha[0] = 5; for (count = 1; count < 5; coun… # What is the output of the following program? #include using namespace std; int main() { int count; int alpha[5]; alpha[0] = 5; for (count = 1; count < 5; count++) { alpha[count] = 5 * count + 10; alpha[count - 1] = alpha[count] - 4; } cout << "List elements: "; for (count = 0; count < 5; count++) cout << alpha[count] << " "; cout << endl; return 0; }

Short answer

The output is: 11 16 21 26 30

Step-by-step solution

Understand the Program Structure

The program initializes an integer array `alpha` of size 5. The first element `alpha[0]` is set to 5. A `for` loop is used to calculate the values of the other elements of the array, followed by a `for` loop to print all the elements.

Initialize and Calculate Array Elements

The first `for` loop runs with `count` starting at 1 up to 4: - In each iteration, it sets `alpha[count]` to `5 * count + 10` and then adjusts `alpha[count - 1]` to be `alpha[count] - 4`. - This results in updating both the current and previous elements of the array in each loop.

Compute Array Elements

Let's compute the array step-by-step through each iteration of the first loop: - **Iteration 1 (count = 1):** - `alpha[1] = 5 * 1 + 10 = 15` - `alpha[0] = 15 - 4 = 11` (overwrites the initial 5 at `alpha[0]`) - **Iteration 2 (count = 2):** - `alpha[2] = 5 * 2 + 10 = 20` - `alpha[1] = 20 - 4 = 16` - **Iteration 3 (count = 3):** - `alpha[3] = 5 * 3 + 10 = 25` - `alpha[2] = 25 - 4 = 21` - **Iteration 4 (count = 4):** - `alpha[4] = 5 * 4 + 10 = 30` - `alpha[3] = 30 - 4 = 26`

Print Array Elements

The second `for` loop outputs the values of the `alpha` array: - Prints each element of the array from index 0 to 4, separated by spaces. - Thus, the output will be the sequence of updated values of the array `alpha`: 11 16 21 26 30.

Key concepts

Array Indexing

In C++, arrays are collections of elements, typically of the same data type, stored in contiguous memory locations. Understanding array indexing is crucial for accessing these elements. Each element in an array can be accessed using an index, which is zero-based in C++. This means the first element is at index 0, the second element is at index 1, and so forth.
For instance, in the given code, `alpha[5]` is an integer array, and `alpha[0]` accesses the first element of the array, setting it to 5 initially. As we proceed through the loop, we access and modify elements using indices like `alpha[count]` and `alpha[count - 1]`. This is crucial because it allows the program to directly read from and write to specified positions in the array. Proper indexing lets you efficiently manage and alter data within an array.

For Loop

The `for loop` in C++ is an essential control structure that allows you to execute a block of code repeatedly, with a specified condition. It's especially useful for iterating over elements in arrays.
In the exercise, there are two main `for loops`. The first initializes array elements based on the index and modifies previous values. This loop starts at `count = 1` and iterates while `count` is less than 5. The loop uses the equation `alpha[count] = 5 * count + 10` to populate the array, while also adjusting the previous array index value with `alpha[count - 1] = alpha[count] - 4`.
Then, the second `for loop` outputs the array values, iterating from `count = 0` to `count < 5`. This exemplifies how `for loops` efficiently cycle through array indices.

Program Output

The output of a C++ program is the result of executing its statements. The exercise involves calculating values and outputting an integer array's contents formatted as a list.
During execution, the first `for loop` alters the contents of the array iteratively. By recalculating values for each index and influencing previous ones, it prepares the array.

• Iteration 1 results in values `11` and `15` for indices `0` and `1`, respectively.
• Iteration 2 results in `16` and `20` for indices `1` and `2`.
• Iteration 3 changes them to `21` and `25` for indices `2` and `3`.
• Iteration 4 gives `26` and `30` for indices `3` and `4`.

The second `for loop` then prints out the entire array: `11 16 21 26 30`, showcasing the altered array contents sequentially.

Namespace std

In C++, `namespace std` is a fundamental concept used to avoid conflicts caused by identical names for entities like functions, variables, etc., across different libraries and classes. The `std` namespace includes most standard C++ library constructs.
By using `namespace std`, as in our exercise, the code can leverage standard library functionality without explicitly prefixing each command with 'std::'. For example, `cout` is a standard output stream object included in the `iostream` library, which is part of `namespace std`. If `namespace std` wasn't used, each standard function would need to be prefixed with `std::`, such as `std::cout` to print to the console.

• This reduces clutter and makes the code more readable.
• However, it is essential to be cautious to prevent name conflicts in larger programs.

Using `namespace std` efficiently enables access to C++ standard features like input/output streams and other utilities.