Module 6 - While-Loop

Question 1

What are the two types of loops?

Answer 1

Condition-controlled and count-controlled

Question 2

Often we have to write code that performs

the same task multiple times. What are the disadvantages of duplicating code?

Answer 2

1. It makes the program large
2. Time-consuming
3. May need to be correct in many places

Question 3

What is the ‘while’ loop?

Answer 3

While condition is true, do task

Question 4

What are the two parts of the while loop?

Answer 4

Test condition for true or false
If true, do the task and test again.
If false, exit structure.

Question 5

What is the syntax for the while loop?

Answer 5

while condition:

____statements

Question 6

What does a while loop look like in a flowchart?

Answer 6

Condition is in a diamond, if true, statements and go back to the start. If false, exit.

Question 7

What is an iteration?

Answer 7

One execution of the body of the loop

Question 8

Why is a ‘while’ loop considered a pretest loop?

Answer 8

1. It won’t execute if condition is false to begin with

2. Requires some steps before the loop

Question 9

What is an infinite loop?

Answer 9

While Loops have something in the code that eventually makes the condition FALSE, thereby stopping the loop.
Infinite loops don’t stop until program is interrupted
It occurs when programmer FORGETS to add that code

Question 10

How do you avoid an infinite loop?

Answer 10

Make sure to change the while condition variable in the loop code

Question 11

What are the two elements of a running total?

Answer 11

1. A loop that reads each number in a series

2. An accumulator variable

Question 12

What are 4 loop best practices?

Answer 12

1. For variables that are changed inside the loop, initialize them BEFORE the loop
2. Ensure while condition starts at TRUE
3. Ensure while condition uses a variable that is CHANGED inside the loop
4. Don’t place code in the loop unless it’s needed (e.g., printing the final result)

Question 13

What are the augmented assignment operators (aka shorthand operators)?

Answer 13

\+= 
-=
*=
/=
%= 

for example, x = x+5 would be x += 5

Question 14

What is a sentinel?

Answer 14

Special value that marks the end of a sequence of items

When the program reaches this value, it knows the end of the sequence was reached and the loop terminates

Question 15

What are examples of sentinels?

Answer 15

Empty line, -1, empty string for input values, etc.

Sentinel value must be DISTINCT from other values so that you can’t confuse with it an actual value in the sequence

Question 16

T or F: Computer can tell the difference between good data and bad data

Answer 16

False. It can’t tell.

If user provides bad input, program will produce bad output. (Garbage in, garbage out)

Question 17

It is important to design programs such that bad input is never accepted. What’s one way to accomplish this?

Answer 17

Input validation - inspecting input before it is processed by the program.
If input is invalid, prompt user to enter correct data
Can use ‘While loop’ to repeat as long as input is bad

Question 18

What is an update assignment?

Answer 18

An assignment where the new value of the variable depends on the old.

Question 19

What is initialization?

Answer 19

An assignment that gives an initial value to a variable that will be updated.
It’s like introducing a variable

Question 20

What is ‘break’?

Answer 20

Way to break the while loop w/ an if statement
while condition:
\_\_\_\_statements
\_\_\_\_if condition:
\_\_\_\_\_\_\_\_break
\_\_\_\_statements (part of while loop)

Question 21

What are the benefits of using a ‘break’ statement?

Answer 21

You can express the stop condition affirmatively (“stop when this happens”) rather than negatively (“keep going until that happens”)

Question 22

What is an algorithm?

Answer 22

A mechanical process for solving a category of problems

No intelligence required, process w/ steps according to a simple set of rules

Question 23

What does ‘eval’ do?

Answer 23

Takes a string and evaluates it using python interpreter
eval(“1+2*4”)
9
*MUST BE STRING