Chapter 5 - Repetition Structures

repetition structure

causes a statement or set of statements to execute repeatedly

condition-controlled loop

uses a true/false condition to control the number of times that it repeats

count-controlled loop

repeats a specific number of times

while loop

consists of a condition that is tested for a true or false value and a statement or set of statements that is repeated as long as the condition is true

What is the output for this code?

spam = 0

while spam < 5:
	print("Hello, World.")
	spam = spam + 1

Hello, World.

Hello, World.

Hello, World.

Hello, World.

Hello, World.

pretest loop

a loop that tests its conditions before performing an iteration

ex: while loops

True or false: loops don’t need a way to terminate

false

infinite loops

loops that continue to repeat until the program is interrupted

• usually occur when the programmer forgets to write code inside the loop that makes the condition false

for loop

used to iterate over a sequence and execute a block of code for each item in that sequence

target variable

the variable that is used in the for clause; it is the target of an assignment at the beginning of each loop iteration

What is the output of this code?

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
	print(fruit)

apple

banana

cherry

True or false: the values that appear in a list do not have to be a consecutively ordered series of numbers

true

range()

generates a sequence of integers within a specified range

range() syntax

range(start, stop, step)

• start and step are optional

Which part of the range() function is inclusive?

start

Which part of the range() function is exclusive?

stop

What is the default for start in the range() function?

0

What is the default for step in the range() function?

1

How do you use decrements in the range() function?

by using a negative step value

What is the output for this code?

for n in range(0,5):
	print(n)

0

1

2

3

4

What is the purpose of the target variable in a for loop?

to reference each item in a sequence of items as the loop iterates

running total

a sum of numbers that accumulates with each iteration of a loop

accumulator

the variable used to keep the running total

What does the accumulator contain when the loop finishes?

the total of the numbers that were read by the loop

What happens if the accumulator starts with any value other than 0?

it will not contain the correct total when the loop finishes

sentinel

a special value that marks the end of a sequence of values

input validation

the process of inspecting data that has been input to a program, to make sure it is valid before it is used in a computation

nested loop

a loop inside another loop

How many times does the inner loop go through all its iterations?

for every single iteration of an outer loop

True or false: inner loops complete their iterations faster than outer loops

true

How do you get the total number of iterations for a nested loop?

multiply the number of iterations of all the loops