Question

Given the variable initializations int \(a[5]=\\{0,10,20,30,40\\}\) int \(k=3\) int \(* p=a+1\) determine the output from each of the following statements: A) cout \(<

Short answer

To sum up, the outputs of each given statement are as follows: A: 30 B: 30 C: 0 D: 0 E: 20 F: 10 G: 10 H: 20

Step-by-step solution

1. Evaluate statement A: cout

To evaluate `a[k]`, we need to find the value stored at index k in array a: a[3]. The array a has the values \(\{0,10,20,30,40\}\). At index 3, element 30 is stored. So the output for this statement would be 30.

2. Evaluate statement B: cout

In this statement, we first find the value of `a+k`. Remember that in C++, the name of an array gives the address of its 0th element, thus a = &a[0]. Therefore, `a+k` means the memory address of the element at index k (a[3]). Then *(a+k) dereferences this memory address, giving us the value stored in a[3]. So the output would be 30.

3. Evaluate statement C: cout

`*a` is equivalent to `*(&a[0])`, which is the value stored in a[0]. In this case, `*a` will result in the value 0. So the output for this statement would be 0.

4. Evaluate statement D: cout

First, find the value of `*a`, which is 0. Then `a[*a]` is equivalent to `a[0]`. In this case, `a[0]` will result in the value 0. So the output for this statement would be 0.

5. Evaluate statement E: cout

First, find the value of `*a`, which is 0. Then `a[*a+2]` evaluates to `a[0+2]`, which is `a[2]`. In this case, `a[2]` will result in the value 20. So the output for this statement would be 20.

6. Evaluate statement F: cout

To evaluate `*p`, we need to remember that p is a pointer initialized to a+1, which points to the second element in the array a with index 1. Thus, *p = a[1], which is the value stored in a[1]. In this case, `a[1]` equals 10, so the output for this statement would be 10.

7. Evaluate statement G: cout

This statement is equivalent to `*(p+0)` since indexing an array in C++ involves pointer arithmetic. Since p is equivalent to a+1, `p[0]` is equivalent to `*(a+1+0)` which is `a[1]`. So the output would be 10.

8. Evaluate statement H: cout

This statement is equivalent to `*(p+1)`. As explained earlier, p is equivalent to a+1, so `p[1]` is equivalent to `*(a+1+1)` which is `a[2]`. In this case, `a[2]` equals 20, so the output for this statement would be 20.

Key concepts

Pointer Arithmetic

Pointer arithmetic in C++ enables us to perform operations on pointers that allow us to navigate through an array or a sequence of memory locations. In the context of arrays, adding an integer value to a pointer shifts the position of the pointer by that number of array elements.

For instance, if we have an integer array defined as int a[5] = {0,10,20,30,40} and a pointer int *p = a + 1, p points to the second element of a because it adds the size of one integer worth of memory to the address of a. When we look at the exercises covered, such as cout << *(a+k) or cout << p[1], the pointer moves to the kth and second index in the array, respectively, and the values 30 and 20 are printed.

Array Indexing

Array indexing is a way to access individual elements within an array using an index number. In C++, an array's index starts from 0, meaning the first element is at index 0, the second at index 1, and so on. In the exercise, when we see statements like cout << a[k] and cout << a[*a+2], we're retrieving the value stored at the kth position, and at the position of *a+2, which is the third element, respectively.

Therefore, accessing an array element a[i] directly gives us the value at the ith position in the array. This method of accessing elements is fundamental in understanding how arrays work in C++.

Dereferencing Pointers

Dereferencing a pointer means obtaining the value stored in the memory location to which the pointer points. The dereference operator (*) is used in C++ to do this. Whenever you see a statement like cout << *p, the program will print the value stored at the address p is pointing to.

In the solutions for statements like cout << *a or cout << *(a+k), we're dereferencing the pointer to get and display the value at the beginning of the array, and the value at the kth position, respectively. Dereferencing is a core concept when it comes to working with pointers and dynamic memory in C++.

C++ Syntax

The syntax in C++ can be rather strict and may seem complex at first, but it's built upon consistent rules. If we break down the exercise statements, they follow specific syntactical patterns of C++. The array declaration int a[5] = {0,10,20,30,40} assigns a block of memory large enough for five integers.

The pointer declaration int *p = a + 1 initializes a pointer p which points to the memory location immediately following a's first element, according to pointer arithmetic rules.

Through these examples, we can see how operators like &, *, and the array index operator [] are used in the language, which illustrates the importance of understanding C++ syntax for effective programming.