Arrays

Question 1

Array

Answer 1

Variable that can store multiple values of the same type

Values are stored in adjacent memory locations

Declared using [ ] operator

Int test [5];

Question 2

A programmer commonly needs to maintain a list of items, just as people often maintain lists of items like a grocery list or a course roster. A

Answer 2

vector is an ordered list of items of a given data type. Each item in a vector is called an element. A programmer must include the statement #include  at the top of the file when planning to use vectors.
vector declaration: 
vector vectorName(numElements)

The statement above declares a vector with the specified number of elements, each element of the specified data type. The type of each vector element is specified within the angle brackets (<>). The number of vector elements is specified within parentheses following the vector name. Ex: vector gameScores(4); declares a vector gameScores with 4 integer elements.

Terminology note: { } are braces. < > are angle brackets, or chevrons. In a vector access, the number in .at() parentheses is called the index of the corresponding element. The first vector element is at index 0.

If you have studied arrays, then know that a vector was added to C++ as a safer and more powerful form of arrays, discussed elsewhere.

Question 3

An element is accessed with

Answer 3

the at() function
vector yearsList(4);

yearsList.at(0) = 1999;

Question 4

A powerful aspect of vectors is that the index is an expression. Ex: userNums.at(i) uses the value held in the int variable i as the index. As such, a vector is useful to easily lookup the Nth item in a list.

Answer 4

A vector’s index must be an unsigned integer type. The vector index cannot be a floating-point type, even if the value is 0.0, 1.0, etc.

The program below allows a user to print the age of the Nth oldest known person to have ever lived. The program quickly accesses the Nth oldest person’s age using oldestPeople.at(nthPerson - 1). Note that the index is nthPerson - 1 rather than just nthPerson because a vector’s indices start at 0, so the 1st age is at index 0, the 2nd at index 1, etc.

Question 5

Declare a vector named myVals that stores 10 items of type int.

Answer 5

vector myVals(10);

Question 6

Assign tempVal with the myVals’ element at the index one after the value held in variable i.

Answer 6

tempVal = myVals.at(i + 1);

Question 7

Iterating through vectors using loops is commonplace and is an important programming skill to master. Because vector indices are numbered 0 to N - 1 rather than 1 to N, programmers commonly use this for loop structure:

Answer 7

// Iterating through myVector
for (i = 0; i < myVector.size(); ++i) {
   // Loop body accessing myVector.at(i

Note that index variable i is initialized to 0, and the loop expression is i < myVector.size() rather than i <= myVector.size(). If myVector.size() were 5, the loop’s iterations would set i to 0, 1, 2, 3, and 4, for a total of 5 iterations. The benefit of the loop structure is that each vector element is accessed as myVector.at(i) rather than the more complex myVector.at(i - 1).

Question 8

True/False: To find the maximum element value, a reasonable statement preceding the for loop is: int maxVal = 0;

Answer 8

False: 0 would yield a wrong final maxVal if all element values were negative. A better statement would be: maxVal = myVctr.at(0).

Question 9

Range-based for loop

Answer 9

The range-based for loop is a for loop that iterates through each element in a vector or container. A range-based for loop is also known as a for each loop. The range-based loop declares a new variable that will be assigned with each successive element of a container, such as a vector, from the first element to the last element.

Question 10

5.5.1: The range-based for loop declares a new variable and assigns the variable with each successive element of a container.

Answer 10

vector teamRoster;

// Adding player names
teamRoster.push_back(“Mike”);
teamRoster.push_back(“Scottie”);
teamRoster.push_back(“Toni”);

cout &laquo_space;“Current roster: “ &laquo_space;endl;

for (string playerName : teamRoster) {
cout &laquo_space;playerName &laquo_space;endl;
}

Question 11

Compared to a regular for loop, a range-based for loop

Answer 11

decreases the amount of code needed to iterate through containers, thus enhancing code readability and clearly demonstrating the loop’s purpose. A range-based for loop also prevents a programmer from writing code that incorrectly accesses elements outside of the container’s range.

Question 12

Modifying vector using range-based for loop

Answer 12

To modify a vector’s elements using a range-based for loop, a programmer must declare the for loop’s variable as a reference. The reference variable will refer to each vector element as the for loop iterates through the vector elements. Assigning the reference variable with a new value assigns the corresponding vector’s element with that value. In the code example below, gradeVal will refer to each vector element, so the statement gradeVal = userGrade; assigns the vector elements with userGrade.

Question 13

Correct for (int &currVal : intValues) starts a range-based for loop that declares a new reference variable &currVal that will refer to each element of the vector intValues. The body of the first loop adds 10 to currVal, which assigns intValues’s corresponding element with that value. The second loop prints out each element of intValues, which has been modified by the first loop.

Answer 13

#include 
#include 
using namespace std;

int main() {
   vector intValues;
   intValues.push_back(3);
   intValues.push_back(9);
   intValues.push_back(7);
   intValues.push_back(4);
   intValues.push_back(1);

for (int &currVal : intValues) {
currVal += 10;
}

for (int intVal : intValues) {
cout &laquo_space;intVal &laquo_space;endl;
}

13
19
17
14
11

Question 14

Range-based for loop with auto

Answer 14

Programmers commonly use the auto type specifier to declare a range-based for loop’s variable. In the code example below, the compiler determines gradeVal is of type double because the elements of the vector examGrades are of type double.

for (auto gradeVal : examGrades) {

Question 15

Commonly, the size of a list of items is not known during a program’s compile time. Thus, a vector’s size need not be specified in the vector’s declaration. Instead, a vector’s size can be set or changed while a program executes

Answer 15

using resize(N). Ex: highScore.resize(10) resizes the highScores vector to have 10 elements.

Question 16

resize() can be called multiple times. If the new size is larger, resize() adds elements at the end. If smaller, resize() deletes elements from the end. If userScores has size 3 (elements 0, 1, 2), userScores.resize(2);

Answer 16

would delete element 2, leaving elements 0 and 1. A subsequent access to userScores.at(2) would result in an error.

Question 17

Appending items to a vector

Answer 17

A programmer can append a new element to the end of an existing vector using a vector’s push_back() function. Ex: dailySales.push_back(521) creates a new element at the end of the vector dailySales and assigns that element with the value 521

Question 18

Table 5.8.1: Functions on the back of a vector.

push_back()

back()

pop_back()

Answer 18

void push_back(const int newVal);
Append new element having value newVal.

int back(); 
Returns vector's last element. Vector is unchanged.

void pop_back(); 
Removes the last element.

Question 19

Element by element vector copy

Answer 19

In C++, the = operator conveniently performs an element-by-element copy of a vector, called a vector copy operation. The operation vectorB = vectorA resizes vectorB to vectorA’s size, appending or deleting elements as needed. vectorB commonly has a size of 0 before the operation.

Question 20

Figure 5.11.4: Vector reversal program with correct output.

Answer 20

int main() {
   const int NUM_ELEMENTS = 8;        // Number of elements
   vector revVctr(NUM_ELEMENTS); // User values
   unsigned int i;                    // Loop index
   int tmpValue;                      // Placeholder

cout &laquo_space;“Enter “ &laquo_space;NUM_ELEMENTS &laquo_space;” integer values…” &laquo_space;endl;
for (i = 0; i < revVctr.size(); ++i) {
cout &laquo_space;“Value: “;
cin&raquo_space; revVctr.at(i);
}

// Reverse
for (i = 0; i < (revVctr.size() / 2); ++i) {
tmpValue = revVctr.at(i); // These 3 statements swap
revVctr.at(i) = revVctr.at(revVctr.size() - 1 - i);
revVctr.at(revVctr.size() - 1 - i) = tmpValue;
}

   // Print values
   cout << endl << "New values: ";
   for (i = 0; i < revVctr.size(); ++i) {
      cout << " " << revVctr.at(i);
   }
   cout << endl;

Question 21

C++ supports two kinds of ordered list types.

Answer 21

Arrays: declared as int myList[10], accessed as myList[i].
Vectors: declared as vector myList(10), accessed as myList.at(i).

Question 22

Conceptually, a two-dimensional array is a table with rows and columns. The compiler maps two-dimensional array elements to one-dimensional memory, each row following the previous row, known

Answer 22

as row-major order.

Question 23

Char arrays were the only kinds of strings in C++’s predecessor language C, and thus are sometimes called

Answer 23

C strings to distinguish them from C++’s string type.

Question 24

Because a string can be shorter than the character array, a string in a char array must end with a special character known as a

Answer 24

null character, written as ‘\0’. Given a string literal like “Star Wars”, the compiler automatically appends a null character.

Question 25

If a char array is initialized when declared, then the char array’s size may be omitted, as in char userName[] = “Hellen”;

Answer 25

The compiler determines the size from the string literal, in this case 6 + 1 (for the null character), or 7.

Question 26

An array of characters ending with a null character is known as a

Answer 26

null-terminated string.

Question 27

An individual array element can be processed like any other type of C++ variable.

Answer 27

True

Question 28

In C++11 the range-based for loop is best used in situations where you need the element subscript for some purpose.

Answer 28

False

Question 29

A vector object automatically expands in size to accommodate the items stored in it.

Answer 29

True

Question 30

By using the same ________ you can build relationships between data stored in two or more arrays.

Answer 30

subscript

Question 31

The name of an array stores the ________ of the first array element.

Answer 31

memory address

Question 32

An array can store a group of values, but the values must be

Answer 32

the same data type

Question 33

An array’s size declarator must be a ________ with a value greater than ________.

Answer 33

constant integer expression, zero

Question 34

Subscript numbering in C++

Answer 34

begins with zero

Question 35

Arrays must be ________ at the time they are ________.

Answer 35

initialized, declared

Question 36

An array can easily be stepped through by using a

Answer 36

a for loop

Question 37

The range-based for loop in C++11 is designed to work with a built-in variable known as

Answer 37

the range variable

Question 38

It is ________ to pass an argument to a function that contains an individual array element, such as scores[3].

Answer 38

legal in C++

Question 39

The ________ is automatically appended to a character array when it is initialized with a string constant.

Answer 39

null terminator

Question 40

When writing functions that accept multi-dimensional arrays as arguments, ________ must be explicitly stated in the parameter list.

Answer 40

all but the first dimension

Question 41

This vector function returns true if the vector has no elements.

Answer 41

empty

Question 42

A vector is an

Answer 42

ordered list of items of a given data type.

Question 43

Each item in a vector is called

Answer 43

an element.

Question 44

A programmer must include the statement

Answer 44

include at the top of the file when planning to use vectors.

Question 45

In a vector access, the number in .at() parentheses

Answer 45

is called the index of the corresponding element. The first vector element is at index 0.

Question 46

A vector’s elements are automatically initialized to

Answer 46

0s during the vector declaration.

Question 47

All of a vector’s elements may be initialized to another single value. Ex: vector myVector(3, -1); creates a vector named myVector with

Answer 47

three elements, each with value -1.

Question 48

A programmer may initialize each vector element with different values by specifying the initial values in braces {} separated by

Answer 48

commas.

Ex: vector carSales = {5, 7, 11}; creates a vector of three integer elements initialized with values 5, 7, and 11.
Such vector declaration and initialization does not require specifying the vector size, because the vector’s size is automatically set to the number of elements within the braces.
For a larger vector, initialization may be done by first declaring the vector, and then using a loop to assign vector elements.

Question 49

Common for loop structure for iterating through a vector.

Answer 49

// Iterating through myVector
for (i = 0; i < myVector.size(); ++i) {
   // Loop body accessing myVector.at(i)
}

Question 50

Accessing an index that is out of range causes the program to automatically abort execution, typically with an error message being automatically printed.

Answer 50

For example, for the declaration vector highScores(8), accessing highScores.at(8), or highScores.at(i) where i is 8, yields the following error message when running the program compiled with g++:

terminate called after throwing an instance of ‘std::out_of_range’
what(): vector::_M_range_check
Abort

DJ - Should be at(7) to account for the (-1) due to index beginning at 0

Question 51

To find the maximum element value, a reasonable statement preceding the for loop is: int maxVal = 0;

Answer 51

False:

0 would yield a wrong final maxVal if all element values were negative. A better statement would be: maxVal = myVctr.at(0).