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Chapter 8: Problem 2

State whether the following are true or false. If the answer is false, explain why. a. The address operator & can be applied only to constants and to expressions. b. A pointer that is declared to be of type void * can be dereferenced. c. Pointers of different types can never be assigned to one another without a cast operation.

Short Answer

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a. False, b. False, c. False.

Step by step solution

01

Address Operator & and Its Usage

The statement is false. The address operator & is not applied to constants or expressions. Instead, it is applied to variables to obtain their memory address. For example, if you have a variable `int x`, you use `&x` to get the address of `x`.
02

Dereferencing a Void Pointer

The statement is false. A pointer of type `void *` cannot be dereferenced because it does not know what type it points to. To dereference it, you must first cast it to another pointer type like `int *` or `char *` that is compatible with the data it points to.
03

Pointer Assignment and Type Casting

This statement is false. In C, pointers to different types can be assigned to one another without using a cast in certain scenarios, such as assigning a `void *` pointer to any other pointer type and vice versa. However, type safety is not guaranteed and is typically done with explicit casting.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Address Operator
In C++, the address operator `&` is a fundamental part of working with pointers. This operator is used to find the memory location of a variable. When you apply it to a variable, like `int a`, using `&a`, you get the address where `a` is stored in memory.
However, it's important to remember that the address operator cannot be applied to constants or complex expressions.
  • It is purely for locating the memory address of a variable.
This feature is what allows pointers to store and reference addresses in C++. Understanding this operator is crucial because it forms the first step in interacting with pointers.
Dereferencing Pointers
Dereferencing is another significant operation when dealing with pointers in C++. It allows you to access or modify the data at the memory location a pointer references. If you have a pointer, like `int *ptr`, you dereference it with the asterisk (*) operator, i.e., `*ptr`, to access the integer value stored.
However, if a pointer is of type `void *`, it cannot be dereferenced directly because `void` does not specify any data type.
  • Before you can dereference a void pointer, you must cast it to another pointer type that reflects the correct data kind, for example, `(int *)` or `(char *)`.
Understand that dereferencing is how you "reach into" the memory location pointed to and extract or manipulate the value, making it an essential process when working with pointers.
Pointer Type Casting
Pointer type casting in C++ is converting a pointer of one type to another. While pointers of different types aren't directly assignable, there are cases where you can indirectly assign them by using casts.
For example, assigning a pointer of type `void *` to a pointer of any other type is permissible without explicit casting in C.
  • Type casting ensures that the pointer behaves according to the type you need it to act as.
  • This operation should be performed cautiously since incorrect casting might lead to undefined behavior.
Type casting pointers is a powerful tool, but it comes with risks and should be applied only when necessary, ensuring type safety is not compromised.

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Most popular questions from this chapter

Write a program that encodes English language phrases into pig Latin. Pig Latin is a form of coded language often used for amusement. Many variations exist in the methods used to form pig Latin phrases. For simplicity, use the following algorithm: To form a pig-Latin phrase from an English-language phrase, tokenize the phrase into words with function strtok. To translate each English word into a pig-Latin word, place the first letter of the English word at the end of the English word and add the letters ay." Thus, the word "jump" becomes "umpjay," the word "the" becomes "hetay" and the word "computer" becomes "omputercay." Blanks between words remain as blanks. Assume that the English phrase consists of words separated by blanks, there are no punctuation marks and all words have two or more letters. Function printLatinword should display each word. [Hint: Each time a token is found in a call to strtok, pass the token pointer to function printLatinword and print the pig-Latin word.]

Write a program that inputs a line of text, tokenizes the line with function strtok and outputs the tokens in reverse order.

For each of the following, write C++ statements that perform the specified task. Assume that double-precision, floating-point numbers are stored in eight bytes and that the starting address of the array is at location 1002500 in memory. Each part of the exercise should use the results of previous parts where appropriate. a. Declare an array of type double called numbers with 10 elements, and initialize the elements to the values 0.0, 1.1, 2.2, ..., 9.9. Assume that the symbolic constant SIZE has been defined as 10. b. Declare a pointer nPtr that points to a variable of type double. c. Use a for statement to print the elements of array numbers using array subscript notation. Print each number with one position of precision to the right of the decimal point. d. Write two separate statements that each assign the starting address of array numbers to the pointer variable nPtr. e. Use a for statement to print the elements of array numbers using pointer/offset notation with pointer nPtr. f. Use a for statement to print the elements of array numbers using pointer/offset notation with the array name as the pointer. g. Use a for statement to print the elements of array numbers using pointer/subscript notation with pointer nPtr. h. Refer to the fourth element of array numbers using array subscript notation, pointer/offset notation with the array name as the pointer, pointer subscript notation with nPtr and pointer/offset notation with nPtr. i. Assuming that nPtr points to the beginning of array numbers, what address is referenced by nPtr + 8? What value is stored at that location? j. Assuming that nPtr points to numbers[ 5 ], what address is referenced by nPtr after nPtr -= 4 is executed? What is the value stored at that location?

For each of the following, write C++ statements that perform the specified task. Assume that unsigned integers are stored in two bytes and that the starting address of the array is at location 1002500 in memory. a. Declare an array of type unsigned int called values with five elements, and initialize the elements to the even integers from 2 to 10. Assume that the symbolic constant SIZE has been defined as 5. b. Declare a pointer vPtr that points to an object of type unsigned int. c. Use a for statement to print the elements of array values using array subscript notation. d. Write two separate statements that assign the starting address of array values to pointer variable vPtr. e. Use a for statement to print the elements of array values using pointer/offset notation. f. Use a for statement to print the elements of array values using pointer/offset notation with the array name as the pointer. g. Use a for statement to print the elements of array values by subscripting the pointer to the array. h. Refer to the fifth element of values using array subscript notation, pointer/offset notation with the array name as the pointer, pointer subscript notation and pointer/offset notation. i. What address is referenced by vPtr + 3? What value is stored at that location? j. Assuming that vPtr points to values[ 4 ], what address is referenced by vPtr -= 4? What value is stored at that location

(Quicksort) You have previously seen the sorting techniques of the bucket sort and selection sort. We now present the recursive sorting technique called Quicksort. The basic algorithm for a single-subscripted array of values is as follows: a. Partitioning Step: Take the first element of the unsorted array and determine its final location in the sorted array (i.e., all values to the left of the element in the array are less than the element, and all values to the right of the element in the array are greater than the element). We now have one element in its proper location and two unsorted subarrays. b. Recursive Step: Perform Step 1 on each unsorted subarray. Each time Step 1 is performed on a subarray, another element is placed in its final location of the sorted array, and two unsorted subarrays are created. When a subarray consists of one element, that subarray must be sorted; therefore, that element is in its final location. The basic algorithm seems simple enough, but how do we determine the final position of the first element of each subarray? As an example, consider the following set of values (the element in bold is the partitioning elementit will be placed in its final location in the sorted array): 37 2 6 4 89 8 10 12 68 45 a. Starting from the rightmost element of the array, compare each element with 37 until an element less than 37 is found. Then swap 37 and that element. The first element less than 37 is 12, so 37 and 12 are swapped. The values now reside in the array as follows: 12 2 6 4 89 8 10 37 68 45 Starting from the left of the array, but beginning with the element after 12, compare each element with 37 until an element greater than 37 is found. Then swap 37 and that element. The first element greater than 37 is 89, so 37 and 89 are swapped. The values now reside in the array as follows: 12 2 6 4 37 8 10 89 68 45 Starting from the right, but beginning with the element before 89, compare each element with 37 until an element less than 37 is found. Then swap 37 and that element. The first element less than 37 is 10, so 37 and 10 are swapped. The values now reside in the array as follows: 12 2 6 4 10 8 37 89 68 45 Starting from the left, but beginning with the element after 10, compare each element with 37 until an element greater than 37 is found. Then swap 37 and that element. There are no more elements greater than 37, so when we compare 37 with itself, we know that 37 has been placed in its final location of the sorted array. Once the partition has been applied to the array, there are two unsorted subarrays. The subarray with values less than 37 contains 12, 2, 6, 4, 10 and 8. The subarray with values greater than 37 contains 89, 68 and 45. The sort continues with both subarrays being partitioned in the same manner as the original array. Based on the preceding discussion, write recursive function quickSort to sort a single subscripted integer array. The function should receive as arguments an integer array, a starting subscript and an ending subscript. Function partition should be called by quickSort to perform the partitioning step
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