Chapter 5

Chapter 5

CONDITIONS, LOGICAL EXPRESSIONS, AND SELECTION CONTROL STRUCTURES

QUESTIONS

True/False

1. An example of a logical (Boolean) expression is an arithmetic expression followed by a relational operator followed by an arithmetic expression.

2. Boolean variables cannot store the result of a comparison of two variables.

3. The only logical expressions that can be assigned to Boolean variables are the literal values TRUE and FALSE.

4. If ch1 contains the value 'C' and ch2 contains the value 'K', the value of the C++ expression

ch1 <= ch2

is 1 (TRUE).

5. If P and Q are logical expressions, the expression P AND Q is TRUE if either P or Q is TRUE or both are TRUE.

6. The expression !(n < 5) is equivalent to the expression n > 5.

7. To test whether someInt equals 25 or 30, the C++ expression

someInt == 25 || 30

has the correct semantics but produces a syntax (compile-time) error.

8. According to DeMorgan's Law, the expression

!(x <= y || s > t)

is equivalent to

x <= y && s > t

9. The statement

if (grade == 'A' || grade == 'B' || grade == 'C')

cout << "Fail";

else

cout << "Pass";

prints Pass if grade is 'A', 'B', or 'C' and prints Fail otherwise.

10. If a C++ If statement begins with

if (age = 30)

the If condition is an assignment expression, not a relational expression.

11. The code segment

if (speed <= 40)

cout << "Too slow";

if (speed > 40 && speed <= 55)

cout << "Good speed";

if (speed > 55)

cout << "Too fast";

could be written equivalently as

if (speed <= 40)

cout << "Too slow";

else if (speed <= 55)

cout << "Good speed";

else

cout << "Too fast";

12. If the code fragment

if (a >= 10)

if (a < 20)

a = a + 2;

else

a = a + 1;

is indented according to the manner in which it is executed, the correct indentation is

if (a >= 10)

if (a < 20)

a = a + 2;

else

a = a + 1;

13. Testing is performed only in the implementation phase of a program's life cycle.

14. Given the module description

PRINT AVERAGE (Level 1)

Print a heading

Print sumOfValues / countOfValues

the following is an appropriate module precondition: "sumOfValues is assigned AND countOfValues does not equal 0."

15. Given the module description

PRINT AVERAGE (Level 1)

Print a heading

IF countOfValues isn't 0

Print sumOfValues / countOfValues

ELSE

Print an error message

the following is an appropriate module precondition: "sumOfValues is assigned AND countOfValues does not equal 0."

Multiple Choice

16. Which of the following does not constitute a logical (Boolean) expression?

a. an arithmetic expression followed by a relational operator followed by an arithmetic expression

b. an arithmetic expression followed by a logical operator followed by an arithmetic expression

c. a Boolean variable or constant

d. a logical expression followed by a binary logical operator followed by a logical expression

e. a unary logical operator followed by a logical expression

17. Which of the following is not a C++ relational operator?

a. ==

b. <

c. !=

d. &&

e. >=

18. If p is a Boolean variable, which of the following logical expressions always has the value FALSE?

a. p && p

b. p || p

c. p && !p

d. p || !p

e. b and d above

19. If DeMorgan's Law is used to negate the expression

(i < j) && (k == l)

then the result is:

a. (i < j) || (k == l)

b. (i > j) && (k != l)

c. (i >= j) || (k != l)

d. (i > j) || (k != l)

e. (i >= j) && (k != l)

20. Given a Boolean variable isEmpty, which of the following is a valid C++ assignment statement? (Assume that TRUE has been defined as the value 1.)

a. isEmpty = TRUE;

b. isEmpty = !isEmpty;

c. isEmpty = m > n;

d. a and b above

e. a, b, and c above

21. Which logical operator (op) is defined by the following table? (T and F denote TRUE and FALSE.)

P Q P op Q

------------

T T T

T F F

F T F

F F F

a. NOT

b. AND

c. OR

d. none of the above

22. Which C++ logical expression correctly determines whether the value of beta lies between 0 and 100?

a. 0 < beta < 100

b. 0 < beta && beta < 100

c. (0 < beta) && (beta < 100)

d. b and c above

e. a, b, and c above

23. This question is about short-circuit evaluation of logical expressions. Consider the following expression in some imaginary programming language (not C++):

(N > 5) AND (K / N < 12)

If N equals 0 when this expression is evaluated, which of the following statements about the expression is true?

a. It causes a divide-by-zero error only if the language uses short-circuit

evaluation.

b. It causes a divide-by-zero error only if the language does not use short-circuit

evaluation.

c. It causes a divide-by-zero error whether or not the language uses short-circuit

evaluation.

d. It never causes a divide-by-zero error.

24. If the int variables i, j, and k contain the values 10, 3, and 20, respectively, what is the value of the following logical expression: j < 4 || j == 5 && i <= k

a. 3

b. FALSE

c. 20

d. TRUE

25. After execution of the following code, what will be the value of angle if the input value is 10?

cin >> angle;

if (angle > 5)

angle = angle + 5;

else if (angle > 2)

angle = angle + 10;

a. 0

b. 5

c. 10

d. 15

e. 25

26. After execution of the following code, what will be the value of angle if the input value is 10?

cin >> angle;

if (angle > 5)

angle = angle + 5;

if (angle > 2)

angle = angle + 10;

a. 0

b. 5

c. 10

d. 15

e. 25

27. After execution of the following code, what will be the value of angle if the input value is 0?

cin >> angle;

if (angle > 5)

angle = angle + 5;

else if (angle > 2)

angle = angle + 10;

else

angle = angle + 15;

a. 0

b. 5

c. 10

d. 15

e. 25

28. After execution of the following code, what will be the value of angle if the input value is 0?

cin >> angle;

if (angle > 5)

angle = angle + 5;

else if (angle > 2)

angle = angle + 10;

a. 0

b. 5

c. 10

d. 15

e. 25

29. What is the output of the following C++ code fragment? (Be careful here.)

int1 = 120;

cin >> int2; // Assume user types 30

if ((int1 > 100) && (int2 = 50))

int3 = int1 + int2;

else

int3 = int1 - int2;

cout << int1 << ' ' << int2 << ' ' << int3;

a. 120 30 150

b. 120 30 90

c. 120 50 170

d. 120 50 70

e. 120 30 70

30. Consider the following If statement, which is syntactically correct but uses poor style and indentation:

if (x >= y) if (y > 0) x = x * y; else if (y < 4) x = x - y;

Assume that x and y are int variables containing the values 9 and 3, respectively, before execution of the above statement. After execution of the statement, what value will x contain?

a. 9

b. 1

c. 6

d. 27

e. none of the above

31. Consider the following If statement, which is syntactically correct but uses poor style and indentation:

if (x >= y) if (y > 0) x = x * y; else if (y < 4) x = x - y;

Assume that x and y are int variables containing the values 3 and 9, respectively, before execution of the above statement. After execution of the statement, what value will x contain?

a. 9

b. -6

c. 6

d. 27

e. none of the above

32. What is the output of the following code fragment if the input value is 20? (Be careful here.)

cin >> someInt;

if (someInt > 30)

cout << "Moe ";

cout << "Larry ";

cout << "Curly";

a. Curly

b. Moe Larry Curly

c. Larry Curly

d. no output; there is a compile-time error

e. no output; there is a run-time error

33. Assuming alpha and beta are int variables, what is the output of the following code (which is indented poorly)?

alpha = 3;

beta = 2;

if (alpha < 2)

if (beta == 3)

cout << "Hello";

else cout << "There";

a. Nothing is output.

b. Hello

c. There

d. HelloThere

34. What does the following statement print? (All variables are of type int.)

if (j < k)

if (k < j)

cout << 1;

else

cout << 2;

else

if (j < k)

cout << 3;

else

cout << 4;

a. It prints nothing unless j equals k.

b. It always prints 4.

c. It prints 2 if j equals k and 4 otherwise.

d. It prints 2 if j < k and 1 if k <= j.

e. It prints 2 if j < k and 4 otherwise.

35. What is the missing If condition in the following code fragment? The program is supposed to halt if the input file does not exist.

ifstream inFile;

inFile.open("myfile.dat");

if ( )

{

cout << "Cannot open input file." << endl;

return 1;

}

a. inFile

b. myfile.dat

c. !inFile

d. !myfile.dat

e. inFile != myfile.dat

36. The phrase "minimum complete coverage" means that we test a program with

a. at least one set of data.

b. data that executes every branch at least once.

c. data that executes all possible combinations of branches at least once.

d. all possible data values.

37. In order to test the boundaries of the following condition, what data values would you use for the variable alpha? ( alpha is of type int.)

alpha >= 1

a. 0, 1, and INT_MAX

b. 1, 2, and INT_MAX

c. INT_MIN, 1, and INT_MAX

d. INT_MIN, 0, 1, and INT_MAX

e. INT_MIN, 1, 2, and INT_MAX

Fill-In

38. A(n) ____________________ expression is an expression composed of logical (Boolean) values and operations.

39. The operators <, ==, >=, and != are examples of ____________________ operators. (Do not answer "binary.")

40. In programming languages that use ____________________ evaluation of a logical expression, evaluation proceeds in left-to-right order and stops as soon as the final truth value can be determined.

41. The operators &&, ||, and ! are known as ____________________ operators.

42. In programming languages that use ____________________ evaluation of a logical expression, all subexpressions are evaluated before applying any logical operators.

43. Write a logical expression that is TRUE if the variable testScore is greater than or equal to 90 and less than or equal to 100: ____________________

44. Write a logical expression that is FALSE if either x or y is equal to 5: ____________________

45. The order in which the computer executes statements in a program is called the ____________________.

46. An If statement is an example of a(n) ____________________ control structure.

47. An If-Then-Else-If structure represents a(n) ____________________-way branch.

The act of using a C++ stream variable in a logical expression as if it were a Boolean variable is called ____________________ of the stream.

49. Any statement used to alter the normally sequential flow of control is called a(n) ____________________.

50. A(n) ____________________ is an assertion that should be true after a module has finished executing.

51. After the code is written in the implementation phase, you should go over it line by line. This process is known as a(n) ____________________.

52. A(n) ____________________ is an assertion that must be true before a module begins executing.

53. Two approaches to program testing are ____________________ coverage and data coverage.

54. A(n) ____________________ is the process of going through the steps of an algorithm to confirm that they produce the required postcondition, given the stated precondition.