Project 4 Loops Solution

Loops ­— statements that repeat




Keep in mind




Before: What happens before the loop starts



During: What happens during the loop






After: What happens after the loop ends.



Two classic problems:




My loop never ends!



You must make sure your statements during the loop include something to update the variable that gets checked for exit.




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:














































1
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:

P 4_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:





































































2
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:




Bonus 1 point




Re-write your while loop as a while True: loop, with a break.



































































































































































Note that these sequences of rolls




all must end with double 6'





















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