Project 4 – Loops

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Project 4 – Loops
Loops — statements that repeat
Keep in mind
➊ Before: What happens before the loop starts
➋ During: What happens during the loop
➌ After: What happens after the loop ends.
Two classic problems:
1. My loop never ends!
You must make sure your statements during the loop
include something to update the variable that gets
checked for exit.
2. My loop never gets started.
Make sure you prepare for the loop:
Zero totals and counters
Do you need to get an initial value before
you enter the loop?
Overview
P4_repeat 4 points
Ask the user for a number
Repeat a block of statements as many times as the
user requested.
P4_for 6 points
Use each item from a list;
No change to item.
Modify the contents of a list
Examine each item in a list using an index to
get the item by number from the list.
P4_while1 7 points
Debug a loop that does not work correctly.
P4_while2 8 points
Create a loop that adds items until some
exit condition is met.
Notes on loops are available in Canvas Modules Week4
Loop_Notes.pdf
P4_repeat
P4_repeat.py 4 points
Create two variables
n The number of times to repeat an action
x A number you will use to calculate some answers
Set n to a number from 10 to 20 a user provides
Set x to 7
1 point
Ask for a number from 10 to 20, such as 15; assign that value to
n.
1 point
Use a for count in range(n) to repeat some statements n times.
1 point
In the body of your loop, calculate answer as the result of raising x
to the count power. print x, the power to which it is raised, and the
result of raising x to a power.
1 point
Print x, the power, the answer.
Output:
2
P4_for.py 6 points:
1 point
Create a list top_movies with the names of your top four films.
1 points
Use a for loop of the "for item in my_list:" style to print the names
of your top movies, like this
1 point
Create this list of numbers
numbers = [7, 11, 30, 19, 22, -3]
The list has some even numbers such as 30, and some odd
numbers such as 7.
If num is an integer (whole number, no decimals), you can tell if it's
even this way
if num % 2 == 0: # even
print(num, "is even")
Your task: modify the numbers list, doubling all the odd
numbers.
If the list was [3, 4, 5], after your program ran, it would be
[6, 4, 10].
2 points
Use a for loop that uses an index that ranges from 0 up to but not
including the length of the numbers list.
1 point
When finished, print the numbers list.
You'll see this:
P4_while1.py 7 points
This program is buggy. Find the bugs, fix them and run the
corrected program.
# p4_while1.py
# Create a list of countries,
# then print each country on a new line
# find and fix the bugs
hint = "Enter name of country or 'quit': "
country_list = [ ]
nation = "None"
while country != "quit"
nation = input(hint)
nation = nation.title()
country_list.append(nation)
print()
print("Countries")
for country in countries:
print(country)
print()
print("Finished")
When you have fixed the bugs (keep testing!), you will get results
like this when running the fixed program:
3
P4_while2.py 8 points
Here you will keep a list of rolls of 2 dice.
1 point
Starting with an empty roll_list, keep adding 2 dice to the list; your
last 2 in the list are double-6.
2 points
After you roll 6-6, add it to your list and stop.
Although there is no guarantee that your program will ever roll a
double 6, each such roll has about 1 chance in 36 of coming up
double-6.
After 24 rolls, the odds are about 50-50 that you have not rolled a
double-6.
After 100 rolls, there about a 6 % chance that you have not yet
rolled a double 6.
Eventually, well before 20,000 rolls of pairs of dice, you are almost
100% sure of getting a pair of 6's
1 point
Your list must end with 6 6.
2 points
When you finally roll a double-6, print the length of the list, and
print the dice list too.
1 point
Remember your first non-comment statement must be
import random
To roll a die
roll_1 = random.randint(1, 6)
1 point
Roll 2 dice to randomly use numbers 1 through 6.
Note that rolling
1 6
6 5 will not end your dice rolling
3 4
6 6 This ends the dice rolls
Your program will look more or less like this:
Another approach is possible:
Store each pair of rolls as a single 2-digit number such as 23 or
66.
Doing so can simplify the testing in your while loop.
Your program output would look somewhat like this:
Note that these sequences of rolls
all must end with double 6'
Bonus 1 point
Re-write your while loop as a while True: loop, with a break.