Supplementary tasks selection statements

Chapter 4: Selection Statements
A. Review
A.1. What do we mean “selection” in selection statements? Introduce at least three use contexts of each
kind of selection statements.
A.2. When should we use if..else.. statements instead of conditional expressions? Give an example for
an illustration.
A.3. What is a multi-way decision? Give an example with if..else.. statements and another one with
switch..case.. statements.
A.4. When should we use if..else.. statements instead of switch..case.. statements? Give an example for
an illustration.
A.5. What is the “fall-through” property of switch..case.. statements? Give an example to illustrate this
property.
B. Practice
B.1. Write selection statements that might be used in the solutions of the problems B.1.1 to B.1.15 in
Chapter 1. Remember to write variable declaration statements before the selection statements if there
is any variable in these selection statements.
B.2. For each following description, write a corresponding selection statement.
B.2.1. If the norm of any vector is zero, let the user know that it is unable to find an angle between that
vector with the other.
B.2.2. Increase the unit price by 10 if the stock level goes below 5.
B.2.3. Double the unit price if the stock level is 1. Otherwise, decrease the stock level by 1 and increase
the unit price by its half.
B.2.4. If a date is 13 and its day is Friday, inform that the day is an unlucky day. Otherwise, it is informed
as a normal day.
B.2.5. If time is morning, introduce “orange, lemon, apple, pineapple”. If time is noon, introduce
“watermelon, apple, grape, coconut, banana”. If time is evening, introduce “plum, durian, melon,
mango”. If time is night, introduce “peach, pear, avocado”.
B.2.6. If the user chooses “open a file”, the user is given a form to enter a file name. If the user chooses
“exit the program”, a prompt about saving the current status of the user is given to the user. If the user
chooses “save”, the current status of the user is saved and the program is closed. Otherwise, the current
status of the user is deleted and the program is closed.

1


B.2.7. If you consume from more than 0 to 10 KW, the lowest price is applied. If you consume from 10 to
50 KW, the second lowest price is applied. If you consume from 50 to 100 KW, the second highest price
is applied. If you consume more than 100 KW, the highest price is applied. And of course, if you consume
0 KW, there is no charge.
B.2.8. If a week is the first week, introduce the course, start the first chapter, and do no homework. If a
week is the second one, continue the first chapter and start doing homework. If a week is the third one,
start the second chapter, review the first chapter, and do homework. If a week is the fourth one,
continue the second chapter and do homework. If a week is the fifth one, start the third chapter, review
the second chapter, start the assignment, and do homework. If the week is the sixth one, continue the
third chapter, keep working on the assignment, and do homework. If the week is the seventh one, start
the fourth chapter, review the third chapter, keep working on the assignment, do homework, and take a
break.
B.3. Identify which statement is correct and which is not. For those incorrect statements, make
appropriate changes so that they become correct. After all, describe the output of each statement.
B.3.1.

B.3.2.

B.3.3.

2


B.3.4.

B.3.5.

3


B.4. Rewrite the following conditional expressions using appropriate if../if..else.. statements. If those
statements are executed, what will be on screen?
B.4.1.

B.4.2.

B.4.3.

B.4.4.

B.4.5.

4


B.5. Rewrite the following switch..case.. statements using appropriate if../if..else.. statements. If those
statements are executed, what will be on screen with different values of the input variable?
B.5.1.

B.5.2.

5


B.5.3.

B.5.4.

6


B.6. In your assignment, you might have a menu listing several options to have access to your program.
The following are some options:
- Populate data
- Query data
- Make simple queries
- Make advanced queries
- Update data
- Insert a new item
- Modify an existing item
- Delete an existing item
- Simulate a control flow
- Exit
Write a program to generate a menu with the aforementioned options in a similar format shown above.
Ask a user about what he/she would like to proceed. Display what he/she has chosen. After that, say
“Thank you!” before asking he/she to press Enter for closing the program. It is supposed that a user can
key what he/she can. Therefore, make sure that you check his/her input carefully and appropriately.
B.7. Write a program to ask a user to input 2 opposite vertices of a 4-sided polygon in an R2 space.
Display the information about a given 4-sided polygon with a header Polygon’s model \t Area \t Type.
7


Area column is with right justification and the others with left justification. Examples are given as
follows:
Polygon’s model
Square

Area
900

Type
medium-sized

Or:
Polygon‘s model

Area

Rectangle

80

Type
small-sized

Or:
Polygon’s model

Area

Type

0

none

Invalid

Polygon’s model is Square, Rectangle, or Invalid. If an area of a polygon is zero, such a polygon has an
invalid polygon’s model and its type is none. If an area of a polygon is in (0, 100), its type is small-sized. If
an area of a polygon is in [100, 10000), its type is medium-sized. Otherwise, its type is large-sized.
It is supposed that a user can key what he/she can. Therefore, make sure that you check his/her input
carefully and appropriately.
B.8. Write a program to ask a user to input 3 vertices of a triangle in an R2 space. Check if a given triangle
is an equilateral, isosceles, squared, squared isosceles, normal, or invalid triangle. An invalid triangle is a
triangle with no area, i.e. 3 vertices lie on the same straight line. Print the information of a given triangle
along with its type using left justification as follows:
The vertices that have been input:
Vertex

X

Y

1

1.0

1.0

2

0

0

3

0

1.0

The triangle that has been form is: squared isosceles.
It is supposed that a user can key what he/she can. Therefore, make sure that you check his/her input
carefully and appropriately.
B.9. It is supposed that each customer is represented with 3 attributes: the number of bought items in a
year, the number of registered services, and the number of shopping times in a year. A valued customer
8


is standardized with (1000, 10, 100) corresponding to the aforementioned 3 attributes and a non-valued
customer with (10, 1, 1) and a potentially valued customer with (500, 5, 50). Given at least 3 customers
each of whom has 3 input attribute values, determine if each of them is a valued customer, a nonvalued customer, or a potentially valued customer based on the most similarity he/she has to a
corresponding standardized customer. The Euclidean distance can be used to express similarity between
a given customer and a standardized customer. The smaller Euclidean distance implies the more
similarity. Display the result in the form of a table with a header such as: CustomerID \t BoughtItem# \t
RegisteredService# \t ShoppingTime# \t Standardized. In the resulting table, BoughtItem#,
RegisteredService#, and ShoppingTime# columns are with right justification and the others with left
justification. An example is given below.
Customer grouping:
CustomerID

BoughtItem#

RegisteredService#

ShoppingTime#

1

1200

9

120

2

12

0

2

3

205

6

50

Standardized
Valued
Non-valued
Potentially valued

Euclidean distance between the first customer and the standardized valued customer is calculated as
follows: (12001000) 2  (9 10) 2  (120100) 2  201 .
It is supposed that a user can key what he/she can. Therefore, make sure that you check his/her input
carefully and appropriately.
B.10. Check your coding style with the programs you have written. Should anything be changed with
your programs so that they can be not only executable but also readable? Rewrite your programs if yes.
NOTE: none of for, while, do..while statements is allowed to be used in your programs in this chapter.

9