Question

What is the output of the following code? int *secret; int j; secret = new int[10]; secret[0] = 10; for (j = 1; j < 10; j++) secret[j] = secret[j - 1] + 5; for (j = 0; j < 10; j++) cout << secret[j] << " "; cout << endl;

Short answer

The output is: 10 15 20 25 30 35 40 45 50 55

Step-by-step solution

Analyze the Array Initialization

First, we initialize a pointer `secret` using dynamic memory allocation for an integer array of size 10 with `new int[10]`. This allocates memory for 10 integers.

Initialize First Element

The code initializes the first element of the array `secret[0] = 10;`. Therefore, `secret[0]` holds the value 10. This serves as the base value for the rest of the array elements.

Populate the Array Elements

A `for` loop starts with `j` initialized to 1 and runs while `j` is less than 10. In each iteration, `secret[j]` is assigned the value of `secret[j-1] + 5`. This means each subsequent element is 5 more than the previous one. The updates will be as follows: - `secret[1] = 15` - `secret[2] = 20` - `secret[3] = 25` - `secret[4] = 30` - `secret[5] = 35` - `secret[6] = 40` - `secret[7] = 45` - `secret[8] = 50` - `secret[9] = 55`

Output the Elements

The second `for` loop iterates over the array from `j = 0` to `j = 9`, printing each element of `secret` followed by a space. The loop, therefore, prints the elements in order and separates them with a space.

Final Array Output

The output of the program is the sequence of numbers produced by the above loops: `10 15 20 25 30 35 40 45 50 55`. This final list is followed by a newline due to the `cout << endl;` statement.

Key concepts

Dynamic Memory Allocation

Dynamic memory allocation is a mechanism by which programs can request memory from the heap at runtime. This is essential when the amount of memory required is not known at compile time, as is the case with arrays whose size needs flexibility.

In C++, dynamic memory allocation is achieved using `new`. In our example:

• `int* secret = new int[10];` requests space for 10 integers.
• The memory allocated is returned through a pointer, `secret`, that will manage it.

Memory stays allocated until it is explicitly released using `delete` or `delete[]`, which we should do in a real-world scenario to avoid memory leaks.

Pointer Initialization

Pointer initialization is crucial for pointer variables in C++. Pointers hold memory addresses, and before using them, they should be initialized to a valid memory location. This prevents undefined behavior.

In our code, `int* secret;` declares a pointer to an integer. Without initialization, `secret` isn't useful until it points to an allocated memory. With `secret = new int[10];`, the pointer `secret` points to the first element of an integer array of size 10.

This practice safeguards against using pointers that reference unallocated memory, ensuring the integrity of your program.

Array Manipulation

Array manipulation in programming refers to how we work with arrays' data, such as modifying, accessing, or iterating over the elements. In C++, arrays are closely tied to pointers.

In the given example, an integer array is manipulated using a simple for loop:

• The first value, `secret[0]`, is set to 10.
• Subsequent elements are calculated by adding 5 to the previous element.
• The loop `for (j = 1; j < 10; j++)` helps in filling the array with values: 15, 20, 25, up to 55.

This step-by-step manipulation demonstrates how we can systematically influence each element's value.

Output Prediction

Predicting a program's output involves understanding what each line of code does and foreseeing the final results presented to the user.

In our example, by examining every element manipulation within the `secret` array, we determine its content after the loop finishes. The final task is to predict the printed output from the `cout` statements.

• The loop: `for (j = 0; j < 10; j++) cout << secret[j] << " ";` executes, printing each element of `secret`.
• The sequence printed is: `10 15 20 25 30 35 40 45 50 55`.

Predicting this output is key to understanding the array's construction and successful execution of loops involved in the exercise.