Variables

Question 1

What is a block?

Answer 1

Also known as a compound statement, it is a group of statements that are surrounded by {}, and are treated by the compiler as a single statement
.

Question 2

What is the recommended maximum depth for nesting blocks, and what should be done when it is reached?

Answer 2

3 - 4 blocks deep, anymore and it’s time for multiple functions.

Question 3

What is a local variable?

Answer 3

A variable inside a code block that has local (also known as block) scope.

Question 4

What happens to local variables when the block ends?

Answer 4

They are destroyed.

Question 5

T/F: Nested blocks are considered part of the outer block in which they are defined

Answer 5

T; variables declared in the outer block can be seen inside the nested block

Question 6

What is the best practice when deciding the scope of a variable?

Answer 6

Give it the smallest possible use depending on where it is used. This avoids confusion and can help with efficiency.

Question 7

What is the scope of a global variable?

Answer 7

Program scope; can be accessed anywhere.

Question 8

T/F: global variables can be accessed across multiple files.

Answer 8

T; they have program scope.

Question 9

What has to be done in order to share a global variable across files?

Answer 9

The ‘extern’ keyword, which tells the compiler you are not declaring a new variable but rather using a variable defined in an external source.

Question 10

How can a global variable be declared in a header file?

Answer 10

Declare the variable in a .h file with the ‘extern’ keyword, then define it in the corresponding .cppfile, WITHOUT the extern keyword

Question 11

In the case that you are working in a block where the a local variable with the same name as a global variable replaces it, what is the operator to access the global version of a variable?

Answer 11

The unary scope operator, although the need to do this indicates poor organization/naming.

Question 12

What are two reasons global variables are dangerous?

Answer 12

They increase complexity because it means a bug can be literally anywhere in the program, since the global variable is in effect everywhere, and they can be changed by any function anywhere, which can lead to unexpected results.

Question 13

What does file scope mean, and how is it different from global scope?

Answer 13

A variable with file scope can be accessed by any function or block within a single file. File scoped variables act exactly like global variables, except their use is restricted to the file in which they are declared (which means you can not extern them to other files)

Question 14

How is a file scoped variable declared?

Answer 14

with the ‘static’ keyword before the typename

Question 15

What are the different meanings of the static keyword, and what determines its function?

Answer 15

Its location in the program; outside of a block it gives a variable file scope, within a block it gives a variable fixed duration, meaning it is NOT destroyed at the end of the block. This is in contrast to the usual automatic duration of a local variable, which is destroyed at the end of the block.

Question 16

include

What does the following program print?

void IncrementAndPrint()
{
    using namespace std;
    static int s_nValue = 1; // fixed duration
    \++s_nValue;
    cout

Answer 16

2
3
4
b/c a static variable in a block has fixed scope, meaning it is only initialized ONCE and persists throughout the program

Question 17

What is one common use for fixed duration (static local) variables?

Answer 17

For generating unique id’s across a file:

int GenerateID()
{
    static int nNextID = 0;
    return nNextID++;
}

Because nNextID is a local variable, it can not be “tampered with” by other functions.

Question 18

Describe implicit type conversion.

Answer 18

Implicit type conversion is done automatically by the compiler whenever data from different types is intermixed. When a value from one type is assigned to another type, the compiler implicitly converts the value into a value of the new type. For example:

double dValue = 3; // implicit conversion to double value 3.0

int nValue = 3.14156; // implicit conversion to integer value 3

Question 19

What is widening?

Answer 19

In any operation involving two or more operands with at least two different types, the operand with the smallest data type is converted to the larger data type to minimize data loss.

Question 20

What is wrong with the following conversion:

float fValue = 10 / 4;

Answer 20

10 and/or 4 need to first be cast as floats, otherwise the expression will first evaluate to 2 (without the fractional component), and the float cast will merely convert 2 to 2(.0)

Question 21

What is the syntactical difference between a standard cast and a C-style cast?

Answer 21

Both are explicit type conversions.

Standard cast:
(castType)varName

C-style cast (more function-like):
castType(varName)

Question 22

What is a static cast?

Answer 22

It is used to tell the compiler you want to convert a value of one type to a type with a smaller range, even though this can cause data loss:

int nValue = 48;
char ch = static_cast(nValue);

Question 23

What is an enumerated type?

Answer 23

A simple way to, in C++, create a new data type. An enumerated type is a data type where every possible value is defined as a symbolic constant (called an enumerator)

Question 24

T/F: defining an enumerated type allocates memory.

Answer 24

F; memory is only allocated when a variable of the enumerated type is declared

Question 25

Enum variables have the same size as what other type?

Answer 25

int

Question 26

What are the default values for enum types, and how can values be defined explicitly?

Answer 26

By default, the first value is 0 and increases by 1 for each enumerator. If a value is explicitly defined but the next is not, then the next value will be implicitly defined as one greater than the previous value:

enum Animal
{
    ANIMAL_CAT = -3,
    ANIMAL_DOG, // assigned -2
    ANIMAL_PIG, // assigned -1
    ANIMAL_HORSE = 5,
    ANIMAL_GIRAFFE = 5,
    ANIMAL_CHICKEN // assigned 6
};

Question 27

T/F: You can cast an enum type as an int, but not the other way around.

Answer 27

T

Question 28

Assuming COLOR_BLUE is from an enumerated value but not from the ‘animal’ enum, will the following code compile?

Answer 28

No; each enumerated type is a distinct type

Question 29

What are some good uses for enum types?

Answer 29

Array indices, error code return values

Question 30

What is a typedef and what is its syntax?

Answer 30

Typedefs allow the programmer to create an alias for a data type, and use the aliased name instead of the actual type name:

typedef long miles; // define miles as an alias for long

// The following two statements are equivalent:
long nDistance;
miles nDistance;

Question 31

What is a smart use of typedefs?

Answer 31

To make code more legible:

typedef long miles;
typedef long speed;

miles nDistance = 5;
speed nMhz = 3200;

// The following is okay, because nDistance and nMhz are both type long
nDistance = nMhz;

Note that, because the underlying types are identical, the last statement in the above example is acceptable.

Question 32

Why are typedefs extremely useful for maintaining code?

Answer 32

It allows you to change the underlying type of an object without having to change lots of code. For example, if you were using a short to hold a student’s ID number, but then decided you needed a long instead, you’d have to comb through lots of code and replace short with long. However, with a typedef, all you have to do is change typedef short studentID to typedef long studentID and you’re done.

Question 33

Explain the following example:

#ifdef INT_2_BYTES
typedef char int8;
typedef int int16;
typedef long int32;
#else
typedef char int8;
typedef short int16;
typedef int int32;
#endif

Answer 33

It allows for platform independent coding by ensuring that, if the size of an int is 2 bytes instead of the usual 4, an int will not be used to store more than 2 bytes of information, as data loss will occur otherwise.

Question 34

What is an aggregate data type?

Answer 34

A data type that groups multiple individual variables together.

Question 35

What is a struct?

Answer 35

An aggregate data type which allows us to group variables of mixed data types together into a single unit

Question 36

What are the variables inside a struct known as?

Answer 36

Members

Question 37

When is memory allocated to a struct type?

Answer 37

When a variable of the struct’s type is declared, NOT when the struct is defined.

Question 38

How can the values of struct members be set?

Answer 38

With the member selection operator:

structVar.memberName = value

Question 39

T/F: An entire struct can be passed as a parameter

Answer 39

T; the function can then access the members of the struct

Question 40

In the case that a struct contains another struct, how can the members of the inner struct be accessed?

Answer 40

With two ‘.’s:

struct Company
{
    Employee sCEO; // Employee is a struct within the Company struct
    int nNumberOfEmployees;
};

Company sMyCompany;

Question 41

What is an initializer list, and what is its syntax?

Answer 41

It is a way to quickly set all the members of a struct when declaring a new variable of the struct’s type:

struct Employee
{
    int nID;
    int nAge;
    float fWage;
};

Employee sJoe = {1, 42, 60000.0f};

Question 42

T/F: You cannot initialize a struct within a struct with an inner initializer list.

Answer 42

F; the following is valid:

struct Employee
{
    int nID;
    int nAge;
    float fWage;
};

struct Company
{
    Employee sCEO; // Employee is a struct within the Company struct
    int nNumberOfEmployees;
};

Company sCo1 = {{1, 42, 60000.0f}, 5};

Question 43

Where is the best place to declare structs?

Answer 43

A header file