Question

What is the output of the following C++ code? int num; int *listPtr; int *temp; listPtr = new int[5]; num = 8; temp = listPtr; for (int j = 0; j < 5; j++) { *listPtr = num; num = num + 2; listPtr++; } listPtr = temp; for (int k = 0; k < 5; k++) { *temp = *temp + 3; temp++; } for (int k = 0; k < 5; k++) { cout << *listPtr << " "; listPtr ++; } cout << endl;

Short answer

11 13 15 17 19

Step-by-step solution

Initialize variables and allocate memory

Four variables are initialized: an integer `num`, two integer pointers `listPtr` and `temp`, and an array of integers of size 5 is allocated and pointed to by `listPtr`. The variable `num` is assigned the value 8.

Fill array with incrementing values

A loop runs through indices 0 to 4. In each iteration, the value of `num` is assigned to the memory location pointed by `listPtr`, and then `num` is incremented by 2. `listPtr` is incremented by 1 each iteration, effectively moving the pointer to the next element in the array.

Reset listPtr to start of the array

The pointer `listPtr` is reset to the beginning of the array by assigning it the value of `temp`, which was initially set to `listPtr`.

Increment each array element by 3

A loop iterates through the array, incrementing each element in the array by 3. The pointer `temp` is used to traverse and modify the array.

Print modified array

Finally, a loop prints each element of the array. The pointer `listPtr` is used to traverse and output the array contents.

Key concepts

Memory Allocation

Memory allocation in C++ is a fundamental concept that involves reserving space in memory for variables, arrays, and data structures. In the provided code, dynamic memory allocation is demonstrated using the `new` keyword.
This keyword requests a block of memory from the free store (also known as the heap), allowing for the creation of an array of integers:

• The statement `listPtr = new int[5];` allocates an array of five integers.
• The pointer `listPtr` holds the address of the first element of this array.
• This memory remains allocated until it is explicitly deallocated (though the code here does not show the deletion).

Understanding dynamic memory allocation ensures we efficiently manage memory, which is crucial for avoiding memory leaks and optimizing program performance.

Pointer Arithmetic

Pointer arithmetic involves operations on pointer values and is integral to navigating arrays in C++. When you increment or decrement a pointer, you change its address to point to another element in a data structure. In the example code:

• The loop `for (int j = 0; j < 5; j++)` uses `listPtr++` to move the pointer from one array element to the next.
• Each `listPtr++` effectively increments the pointer by the size of an integer (typically four bytes), positioning it at the next element in the array.
• This allows you to traverse the array efficiently with minimal code.

This pointer arithmetic enables flexible manipulation of data without needing explicit array indices, which can make code more elegant and generally faster.

Incrementing Values

Incrementing values is a straightforward operation but can be extremely powerful in programming loops and array operations. In our exercise, we see:

• The integer `num` is initially set to 8 and then incremented by 2 in each loop iteration (`num = num + 2`).
• After filling the array with these values, each element is further incremented by 3 using another loop (`*temp = *temp + 3`).

This operation, when paired with pointers, allows direct manipulation of data stored in memory, providing means to dynamically adjust data during runtime.
Such practices are commonly used in algorithms that require specific arithmetic transformations of data arrays.

Array Traversal

Array traversal is the process of accessing each element of an array to perform computations or modifications. In this exercise, array traversal is highlighted in two significant loops:

• First loop: Uses `listPtr` to access and rather populate each element with the current `num` value, incrementing `listPtr` as it goes along.
• Second loop: Applies similar traversal to adjust values by adding 3 to each element using `temp`, ensuring `temp` points to the correct elements.
• Final loop: Traverses using `listPtr` again to print each value, providing the modified array's output.

Efficient traversal is critical for processing arrays quickly and is often the backbone of many algorithms.
These loops illustrate classic examples of traversal, important for sorting, searching, or applying transformations to data within arrays.