Variables and Decisions

Question 1

In a program, a (_____) is a named item, such as x or numPeople, used to hold a value.

Answer 1

variable

Question 2

An (_______) assigns a variable with a value, such as x = 5. That assignment means x is assigned with 5, and x keeps that value during subsequent assignments, until x is assigned again.

Answer 2

assignment

Question 3

In programming, = is an (______) of a left-side variable with a right-side value. = is NOT equality as in mathematics. Thus, x = 5 is read as “x is assigned with 5”, and not as “x equals 5”. When one sees x = 5, one might think of a value being put into a box.

Answer 3

assignment

Question 4

What are the basic fundamental data types in C++?

Answer 4

Name Description Size* Range*
char Character or small integer. 1byte signed: -128 to 127
unsigned: 0 to 255

short int (short)	Short Integer.	2bytes	signed: -32768 to 32767
unsigned: 0 to 65535

int Integer. 4bytes signed: -2147483648 to 2147483647
unsigned: 0 to 4294967295

long int (long)	Long integer.	4bytes	signed: -2147483648 to 2147483647
unsigned: 0 to 4294967295

bool Boolean value. It can take one of two values: true or false. 1byte true or false

float Floating point number. 4bytes +/- 3.4e +/- 38 (~7 digits)

double Double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits)

long double Long double precision floating point number. 8bytes +/- 1.7e +/- 308 (~15 digits)

wchar_t Wide character. 2 or 4 bytes 1 wide character

Question 5

A(n) ________ represents a storage location in the computer’s memory.

Answer 5

Variable

Question 6

Data items whose values do NOT change while the program is running are

Answer 6

literals

Question 7

You must have a ________ for every variable you intend to use in a program

Answer 7

variable definition

Question 8

What are the rules of a variable identifier

Answer 8

Neither spaces nor punctuation marks or symbols can be part of an identifier.

Only letters, digits and single underscore characters are valid.

In addition, variable identifiers always have to begin with a letter. They can also begin with an underline character (_ ), but in some cases these may be reserved for compiler specific keywords or external identifiers, as well as identifiers containing two successive underscore characters anywhere. In no case can they begin with a digit

Question 9

Besides the decimal number system that is most common (base 10), two other number systems that can be used in C++ programs are

Answer 9

octal and hexadecimal

Question 10

Which of the following lines must be included in a program that has string variables?

Answer 10

include

Question 11

As you may see in the previous example, strings can be initialized with any valid string literal just like numerical type variables can be initialized to any valid numerical literal. Both initialization formats are valid with strings:

Answer 11

string mystring = "This is a string";
string mystring ("This is a string");

Question 12

A programmer should choose a variable’s type based on the type of value held.

Answer 12

Integer variables are typically used for values that are counted, like 42 cars, 10 pizzas, or -95 days.
Floating-point variables are typically used for measurements, like 98.6 degrees, 0.00001 meters, or -55.667 degrees.
Floating-point variables are also used when dealing with fractions of countable items, such as the average number of cars per household.

Question 13

Branch basics (If)

Answer 13

In a program, a branch is a sequence of statements only executed under a certain condition. Ex: A hotel may discount a price only for people over age 60. An if branch is a branch taken only IF an expression is true.

Question 14

If-elseif-else branches

Answer 14

s. An if-else can be extended to an if-elseif-else structure. Each branch’s expression is checked in sequence; as soon as one branch’s expression is found to be true, that branch is taken. If no expression is found true, execution will reach the else branch, which then executes.

Question 15

What is a flag?

Answer 15

Generally flag is a variable which signels that some event happened (flag raised) or not.

Question 16

isalpha(c) true if alphabetic:

Answer 16

a-z or A-Z
isalpha(‘x’) // true
isalpha(‘6’) // false
isalpha(‘!’) // false

Question 17

isdigit(c) true if digit: 0-9.

Answer 17

isdigit(‘x’) // false

isdigit(‘6’) // true

Question 18

isspace(c) true if whitespace.

Answer 18

isspace(‘ ‘) // true
isspace(‘\n’) // true
isspace(‘x’) // false

Question 19

toupper(c) Uppercase version

Answer 19

letter = toupper('a')  // A
letter = toupper('A')  // A
letter = toupper('3')  // 3

Question 20

tolower(c) Lowercase version

Answer 20

letter = tolower('A')  // a
letter = tolower('a')  // a
letter = tolower('3')  // 3

Question 21

Given string userString is “Run!”. Indicate char x’s value.

x = userString.at(0);

Answer 21

0 is the index of the string’s first character, which is R.

Question 22

A character in a string can be assigned. If userString is “abcde”, then userString.at(3) =

Answer 22

‘X’ yields “abcXe”.

Question 23

Determining the last character in a string is often useful. If a string’s length is known, the last character is at index length - 1.

Answer 23

Ex: “Hey” has length 3, with y at index 2. The function s1.size() returns s1’s length. Ex: If s1 is “Hey”, s1.size() returns 3.

Question 24

A common task is to append (add to the end) a string to an existing string.

Answer 24

The function s1.append(s2) appends string s2 to string s1. Ex: If s1 is “Hey”, s1.append(“!!!”) makes s1 “Hey!!!”.

Question 25

The size() and length() functions both return a string's length.
 Ex: For the string firstName = "Tosi", firstName.size() and firstName.length() both return

Answer 25

4.

Question 26

A common error is to access an invalid string index, especially exactly one larger than the largest index. Given userText with size 8, the range of valid indices are 0 … 7; accessing with index 8

Answer 26

is an error

Question 27

The .at(index) function generates an exception if the index is out of range for the string’s size. An exception is

Answer 27

a detected runtime error that commonly prints an error message and terminates the program.

Question 28

C++ also supports C-style access of a string using brackets [] rather than .at(), as in: someString[0]. However, such C-style access does

Answer 28

not provide such error checking. Good practice is to use .at() rather than brackets for accessing a string’s characters, due to .at()’s error checking.

Question 29

More string operations

find() find(item) returns index of first item occurrence, else returns string::npos (a constant defined in the string library). Item may be char, string variable, string literal (or char array).

substr() substr(index, length) returns substring starting at index and having length characters.

Answer 29

find(item, indx) starts at index indx.
// userText is “Help me!”
userText.find(‘p’) // Returns 3
userText.find(‘e’) // Returns 1 (first occurrence of e only)
userText.find(‘z’) // Returns string::npos
userText.find(“me”) // Returns 5
userText.find(‘e’, 2) // Returns 6 (starts at index 2)

// userText is “http://google.com”
userText.substr(0, 7) // Returns “http://”
userText.substr(13, 4) // Returns “.com”
userText.substr(userText.size() - 4, 4) // Last 4: “.com”

Question 30

Table 3.16.2: String modify functions, invoked as myString.push_back(c). Each increases/decreases string’s length appropriately.
push_back() push_back(c) appends character c to the end of a string.

// userText is “Hello”
userText.push_back(‘?’); // Now “Hello?”
userText.size();

insert() insert(indx, subStr) Inserts string subStr starting at index indx.
// userText is “Goodbye”
userText.insert(0, “Well “);

// userText is “Goodbye”
userText.insert(4, “—”); // Now “Good—bye”
replace() replace(indx, num, subStr) replaces characters at indices indx to indx+num-1 with a copy of subStr.
// userText is “You have many gifts”
userText.replace(9, 4, “a plethora of”);
// Now “You have a plethora of gifts”
str1 + str2

If one of str1, str2 is a string, the other may be a character (or character array).	
// userText is "A B"
myString = userText + " C D";
// myString is "A B C D"
myString = myString + '!';
// myString now "A B C D!"
myString = myString + userText;

Answer 30

// Returns 6

// Now “Well Goodbye”

Returns a new string that is a copy of str1 with str2 appended.

// myString now “A B C D!A B”

Question 31

if else syntax

Answer 31

if (condition) {
  myVar = expr1;
}
else {
  myVar = expr2;
}

Question 32

If-else statements with the form shown below are so common that the language supports the shorthand notation shown.

if (condition) {
  myVar = expr1;
}
else {
  myVar = expr2;
}

Answer 32

myVar = (condition) ? expr1: expr2

A conditional expression has the form condition ? exprWhenTrue : exprWhenFalse.

Question 33

Floating-point numbers should be compared for “close enough” rather than exact equality. Ex: If (x - y) < 0.0001, x and y are deemed equal.

Answer 33

Because the difference may be negative, the absolute value is used: fabs(x - y) < 0.0001. fabs() is a function in the math library. The difference threshold indicating that floating-point numbers are equal is often called the epsilon. Epsilon’s value depends on the program’s expected values, but 0.0001 is common.

The std::abs() function is overloaded to support floating-point and integer types. However, good practice is to use the fabs() function to make the operation clear.