Chapter 3 part 3

Question 1

What is an augmented assignment?

Answer 1

An abbreviated assignment expressions in which the same varianble name appears on the left and right of the assignment’s =, as total does in:
In [1]: for number in [1, 2, 3, 4, 5]:
…….. …….total += number # add number of total and store in number
In [2]: total
Out[2]: 15

Note that this is not in range and is added like normal
0 + 1 + 2 + 3 + 4 + 5 = 15
The += snipper first adds numbers value to the current total, then stores the new value in total

Question 2

Fill in the blank

If x is 7, the value of x after evaluating x *= 5 is .____……_____…____

Answer 2

35

Question 3

Create a variable x with the value 12. Use an exponentiation augmented assignment statement to square x’s value. Show x’s new value.

Answer 3

x = 12
x **= 2
144

Question 4

What does this operator do? //=

Answer 4

Floor division, divides 2 numbers and rounds down the result to the nearest whole number
Ex:
print(7//2)
Out: 3

Question 5

What does this operator do? **=

Answer 5

It uses an exponent
Ex:
12 **= 2
144

Question 6

What does this operator do? %

Answer 6

Divides two numbers and returns the remainder
Ex:
print(10 % 3)
out: 1

Question 7

Define

Requirements statements

Answer 7

Describes what a program is supposed to do, but not how the program should do it

Question 8

Provide an example of a simple statement requirement

Answer 8

A class of ten students took a quiz. Their grades (integers in the range 0 - 100) are 98, 76, 71, 87, 83, 90, 57, 79, 82, 94. Determine the class average on the quiz
- Once you know the problem’s requirements, then you begin creating an algorithm to solve it. Then you can implement that solution as a program and it must:
- 1. keep a running total of the grades
- 2. calc the average-the total of the grades divided by the number of grades
- 3. display the result

Question 9

Consider the following pseudocode for the algorithm

Answer 9

• Note the mentions of total and grade counter
• We’ll use these in the script to calculate the average
• Variables for totaling and counting normally are initiated to zero

Question 10

What are the 3 phases a script can be decomposed by?

Answer 10

initialization phase
processing phase
termination phase

Question 11

Define

Initialization phase

Answer 11

Creates the variables needed to process the grades and set these variables to appropriate initial values

Question 12

Define

Processing phase

Answer 12

Processes the data, calculating the running total and counting the number of grades processed so far

Question 13

Define

Termination phase

Answer 13

Calculates and displays the class average

Question 14

Breakdown step by step how this code works

Answer 14

Initial state:
- total = 0
- grade_counter = 0
First iteration:
- grade = 98
- total = 0 + 98 = 98
- grade_counter = 0 + 1 = 1
Second iteration:
- grade = 76
- total = 98 + 76 = 174
- grade_counter = 1 + 1 = 2
Final state:
- total = 817 (sum of all grades)
- grade_counter = 10 (number of grades)
Avegare calculation:
- average = total / grade_counter
- = 817 / 10 = 81.7

the part that says “for grade in grades” starts a loop that will go through each element in the grades list. Then the total is added with the += grade starting from 0 to each individual grade until all of them have gone through the loop

Question 15

What is an f-string?

Answer 15

Short for formatted string, allows inserting values into a string. In the previous example, it does this by inserting the value of the average into a string.
- The leter f before the string’s opening quote indicates it’s an f-string
- You specify where to insert values by using placeholders delimited by curly braces ({ and }). The placeholder {average} converts the variable average’s value to a string representation, then replaces {average} with that replacement text

Question 16

A(n) ___.___.____ describes what a program is supposed to do, but not how the program should do it

Answer 16

requirements statement

Question 17

Many of the scripts you’ll write can be decomposed into 3 phases:
a.
b.
c.

Answer 17

initialization
processing
termination

Question 18

Display an f-string in which you insert the values of the variables number1 (7) and number 2 (5) and their product. The displayed string should be
7 times 5 is 35

Answer 18

Question 19

What is a sentinel value? aka signal value, a dummy value or a flag value?

Answer 19

These indicate the “end of data entry” It determines when to stop processing a program so it can move onto to the next program segment

Question 20

What is a indefinite iteration?

Answer 20

It is a sentinel-controlled iteration and the number of iterations is not known before the loop begins executing. Ex:
Develop a class-averaging program that processes an arbitrary number of grades each time the program executes.
– arbitrary

A sentinel value must not be confused with any acceptable input value and should not be considered as another input value

Question 21

What is the top-down portion of stepwise refinement

Answer 21

It is a single statement that conveys the program’s overall function
- it rarely conveys enough detail from which to write a program
- specifies what should be done but not how to implement it
- Begin the refinement process by decomposing the top into a sequence of smaller tasks -divide and conquer

Pseudocode representation of the top ex:
Determine the class average for the quiz

Question 22

Give an example of the first refinement from the pseudocode representation of the top ex:
Determine the class average for the quiz

Answer 22

Initialize variables
Input, sum and count the quiz grades
Calculate and display the class average

• Each refinement represents the complete algorithm
• These pseudocode statements correspond to the three execution phases described in the preceding section. The algorithm does not yet provide enough detail for us to write the Python program, so onto the next refinement

Question 23

What do we need for a second refinement?

Answer 23

Commit to specific variables:
- a grade variable in which each succcessive user input will be stored
- a running total of the grades
- a count of how many grades have been processed
- a variable that contains the calculated average

Question 24

From the first refinement:
Initialize variables
can be refined as:

Answer 24

Initialize total to zero
Initialize grade counter to zero
- Other variables are created when they’re needed

Question 25

From the first refinement:
Input, sum and count the quiz grades
can be refined as follows:

Answer 25

*Input the first grade (possibly the sentinel)
While the user has not enetered the sentinel

…..Add this grade into the running total

….Add one to the grade counter

….Input the next grade (possibly the sentinel)*

Question 26

From the first refinement
Calculate and display the class average
can be refined as follows:

Answer 26

*If the counter is not equal to zero
……. Set the average to the total divided by the grade counter
…….. Display the average
Else
…….. Display “No grades were entered”

Question 27

Refinement completion reminders

Answer 27

• Sometimes more than two refimenets are necessary
• You stop refining when there is enough detail to convert the pseudocode to Python
• You can include blank lines for readability

Question 28

Observe the following sentinel-controlled iteration and examine it

Answer 28

Under # processing phase, the program reads the first value before reaching the while statement. If we had initialized it then that value would have been replaced immediately by this assignment

Question 29

Observe the following sentinel-controlled iteration and discuss how the value input affects the while suite

Answer 29

• The value inpute determines whether the program’s flow of control should enter the while’s suite
• If the condition is false the user entered -1, so the suite does not execute
• If true, the suite executes, addint the grade value to the total and incrementing the grade_counter
• grade is always input immediately before the program tests the whilecondition

Question 30

Observe the following sentinel_controlled iteration and discuss what occurs when a sentinel value is input

Answer 30

• When the sentinel value is input, the loop terminates, and the program does not add -1 to the total
• After the loop terminates, the if…else statements execute

Question 31

How do you format the class average with 2 decimal places?

Answer 31

Using a format specifier that describes how to format the replacement text
In the included image, we used the format specifier .2 and tells Python to format the floating-point number (in this case, the average) to 2 decimal places. f stands for floating-point number
Use for readability and precision

Question 32

Sentinel-controlled repetition is called ___blank___ because the number of repetitions is not known before the loop begins executing

Answer 32

indefinite repetition

Question 33

T/F

Sentinel-controlled repetition uses a counter variable to control the number of times a set of instructions executes

Answer 33

False. Sentinel-control reptitioin terminates reptition when the sentinel value is encountered