How to write code to simulate change in dollars using a vending machine change maker program

Assignment Overview
This assignment will give you more experience on the use of:
1.     integers (int)
2.     floats (float)
3.     strings (str)
4.     conditionals
5.     iteration
 
This is an advance program (with new programming concepts) that you did in the lab for chapter 2. Take time to read the instructions carefully before you attempt to do the exercise. Your program will simulate a simple change maker for a vending machine.   It will start with a stock of coins and dollars.  It will then repeatedly request the price for an item to be purchased or to quit.  If given a price, it will accept nickels, dimes, quarters, one-dollar and five-dollar bills—deposited one at a time—in payment.  When the user has deposited enough to cover the cost of the item, the program will calculate the coins to be dispensed in change.  Alternately, the user can cancel the purchase up until full payment has been deposited, in which case, your program will calculate the coins to be dispensed to refund any partial payment already deposited.  With each purchase, the program will update the stock of coins and dollars.  Before quitting, it will output the remaining stock of coins and dollars.  The specifications are spelled out more thoroughly below.  An example interaction with our program appears at the end of this description. All change and refunds must be in coins only, and must use the minimum number of coins possible.
 
Background
 
The algorithm for calculating the numbers of coins of each denomination to dispense so as to minimize the total number of coins is an example of a greedy algorithm.  Since each coin is at least twice the value of the previous coin, you can start by figuring out the most number of quarters you can dispense (without exceeding the amount), then the most number of dimes, and then the number of nickels.  Knowledge of greedy algorithms is not required to complete this assignment.  If you are curious, you can read http://en.wikipedia.org/wiki/Greedy_algorithm.
 
Project Description / Specification
 
Your program must meet the following specifications:
1.     At program start, assume a stock of 25 nickels, 25 dimes, and 25 quarters.  Print the contents of the stock.
2.     Repeatedly prompt the user for a price in the form xx.xx, where x denotes a digit, or to enter ‘q’ to quit. 
3.     When a price is entered:
a.     Check that the price entered is a (non-negative) multiple of .05 (i.e., it is payable in nickels).  If not, then print an error message and start over requesting either a new price or to quit (indicated by entering a ‘q’).
b.     Print a menu for indicating the coin/bill deposited or to cancel payment.
c.     Prompt for a selection from this menu.
d.     If the user enters an illegal selection, re-prompt for a correct one.
e.     Following each deposit, print the remaining amount owed (indicate the number of dollars and the number of cents).
f.      When full payment has been deposited or a ‘c’ has been entered, determine the coins to be dispensed in change or as refund.  This calculation will depend on the amount to be dispensed and also on the number of coins left in the stock.  For example, the least number of coins needed to make up $1.30 is 6 — 5 quarters and 1 nickel.  But if there are only 3 quarters, 3 dimes, and 10 nickels left in the stock, then the least number is 11 — 3 quarters, 3 dimes, and 5 nickels.
g.     Print the numbers of the coins to be dispensed and their denominations.  (Omit a denomination if no coins of that denomination will be dispensed.)
h.     In case exact payment is deposited, print a message such as "No change."
i.      If the change cannot be made up with the coins remaining, dispense the coins available without exceeding the change amount and indicate the amount still due the user, which will have to be collected from a store manager.  For example, if the stock contains one nickel, no dimes, and a quarter and if the change amount is 15 cents, dispense just the nickel and indicate the user should collect 10 cents from a store manager.
j.      Print the contents of the stock following the transaction.
4.     Just before quitting, print the total amount (the number of dollars and number of cents) left in the stock.
 
Deliverables
 
Exercise3.py – your source code solution (remember to include your group number, group members, the date, and comments in this file).
 
Notes and Hints:
1.	Floating point numbers can be difficult to work with due to imprecision. To avoid imprecision in this program, you can multiply the price by 100, round, and convert to an integer (number of cents).  For example, $1.15 is the same as 115 cents. To see why you need to round, try evaluating 1.15*100 in the Python shell.  Now evaluate round(1.15*100).
2.	The quotient (//) operation for integers will be useful for finding the numbers of each coin.   For example, 195//25 is 7, the most number of quarters in 195 cents.   But be careful—if the stock has fewer than 7 quarters left, you will only be able to dispense the number left in the stock.  For example, if there are only 6 quarters left, then you can dispense only 6 quarters and must use dimes and nickels to make up any remaining change.
3.	When we learn about format strings, we can more easily and elegantly print monetary amounts.  For now, just use the Python print(…) command with appropriate string and/or integer arguments to print the number of dollars and the number of cents. 
4.	You do not need to check for any input errors other than those mentioned in this description. 
5.	The logic for this project is sufficiently complex that you will need to break it into small steps that you can implement incrementally.  After implementing each step, test it thoroughly, back it up by committing your code on GitHub before you implement the next step.  For example, you could:
a.     First implement the logic to initialize the stock, print it, and repeatedly prompt for a price until a ‘q’ is entered; just print the value that was input. Test and commit your code. GitHub keeps the history of your code, you can trace back and see how your code looked like by clicking on the commits and the specific commit. This reveal the code you committed at that particular instance
 
b.     Next, add code to check that the input is a legal price and, if it is not, to prompt for a new value.  Again, just print the value that was input. Test and commit your code.
c.     Next, add code to print the menu of selections. Test and commit your code.
d.     Next, add code to repeatedly prompt the user to deposit a coin until the full amount is collected or a ‘c’ is entered and to print the remaining amount owed after each deposit. Test and commit your code.
e.     Next, add code to update the stock. Test and commit your code.
f.      Next, add code to calculate the change or refund to be dispensed.
g.     Next, add code to calculate the number of coins of each denomination to be dispensed and to update the stock.
h.     Etc.
It is not required that you develop the project exactly in this way.  But if you don’t find a way to incrementally build and test your projects, they generally will be more difficult and take you longer to do.  We also recommend an incremental strategy, not just because it is easier, but also because it allows us to give partial credit.  If you hand in a program that we can run and that meets some, but not all, of the requirements, we can grade what you managed to get working.
 
 
Sample Interaction (user inputs shown in red):
>>> =========================== RESTART ============================
>>>
Welcome to the vending machine change maker program
Change maker initialized.
Stock contains:
   25 nickels
   25 dimes
   25 quarters
   0 ones
   0 fives
 
Enter the purchase price (xx.xx) or `q' to quit: 1.96
Illegal price: Must be a non-negative multiple of 5 cents.
 
Enter the purchase price (xx.xx) or `q' to quit: 1.95
 
Menu for deposits:
  'n' - deposit a nickel
  'd' - deposit a dime
  'q' - deposit a quarter
  'o' - deposit a one dollar bill
  'f' - deposit a five dollar bill
  'c' - cancel the purchase
 
Payment due: 1 dollars and 95 cents
Indicate your deposit: 1
Illegal selection: 1
Payment due: 1 dollars and 95 cents
Indicate your deposit: o
Payment due: 95 cents
Indicate your deposit: o
 
Please take the change below.
   1 nickels
 
Stock contains:
   24 nickels
   25 dimes
   25 quarters
   2 ones
   0 fives
 
Enter the purchase price (xx.xx) or `q' to quit: 3.25
 
Menu for deposits:
  'n' - deposit a nickel
  'd' - deposit a dime
  'q' - deposit a quarter
  'o' - deposit a one dollar bill
  'f' - deposit a five dollar bill
  'c' - cancel the purchase
 
Payment due: 3 dollars and 25 cents
Indicate your deposit: o
Payment due: 2 dollars and 25 cents
Indicate your deposit: d
Payment due: 2 dollars and 15 cents
Indicate your deposit: d
Payment due: 2 dollars and 5 cents
Indicate your deposit: o
Payment due: 1 dollars and 5 cents
Indicate your deposit: d
Payment due: 95 cents
Indicate your deposit: c
 
Please take the change below.
   9 quarters
   1 nickels
 
Stock contains:
   23 nickels
   28 dimes
   16 quarters
   4 ones
   0 fives
 
Enter the purchase price (xx.xx) or `q' to quit: .05
 
Menu for deposits:
  'n' - deposit a nickel
  'd' - deposit a dime
  'q' - deposit a quarter
  'o' - deposit a one dollar bill
  'f' - deposit a five dollar bill
  'c' - cancel the purchase
 
Payment due: 5 cents
Indicate your deposit: f
 
Please take the change below.
   16 quarters
   9 dimes
   1 nickels
 
Stock contains:
   22 nickels
   19 dimes
   0 quarters
   4 ones
   1 fives
 
Enter the purchase price (xx.xx) or `q' to quit: 25
 
Menu for deposits:
  'n' - deposit a nickel
  'd' - deposit a dime
  'q' - deposit a quarter
  'o' - deposit a one dollar bill
  'f' - deposit a five dollar bill
  'c' - cancel the purchase
 
Payment due: 25 dollars and 0 cents
Indicate your deposit: f
Payment due: 20 dollars and 0 cents
Indicate your deposit: f
Payment due: 15 dollars and 0 cents
Indicate your deposit: f
Payment due: 10 dollars and 0 cents
Indicate your deposit: f
Payment due: 5 dollars and 0 cents
Indicate your deposit: c
 
Please take the change below.
   19 dimes
   22 nickels
Machine is out of change.
See store manager for remaining refund.
Amount due is: 17 dollars and 0 cents
 
Stock contains:
   0 nickels
   0 dimes
   0 quarters
   4 ones
   5 fives
 
Enter the purchase price (xx.xx) or `q' to quit: .35
 
Menu for deposits:
  'n' - deposit a nickel
  'd' - deposit a dime
  'q' - deposit a quarter
  'o' - deposit a one dollar bill
  'f' - deposit a five dollar bill
  'c' - cancel the purchase
 
Payment due: 35 cents
Indicate your deposit: q
Payment due: 10 cents
Indicate your deposit: d
 
Please take the change below.
  No change due.
 
Stock contains:
   0 nickels
   1 dimes
   1 quarters
   4 ones
   5 fives
 
Enter the purchase price (xx.xx) or `q' to quit: .35
 
Menu for deposits:
  'n' - deposit a nickel
  'd' - deposit a dime
  'q' - deposit a quarter
  'o' - deposit a one dollar bill
  'f' - deposit a five dollar bill
  'c' - cancel the purchase
 
Payment due: 35 cents
Indicate your deposit: q
Payment due: 10 cents
Indicate your deposit: q
 
Please take the change below.
   1 dimes
Machine is out of change.
See store manager for remaining refund.
Amount due is: 5 cents
 
Stock contains:
   0 nickels
   0 dimes
   3 quarters
   4 ones
   5 fives
 
Enter the purchase price (xx.xx) or `q' to quit: q
 
Total: 29 dollars and 75 cents
>>> 

# welcome the user
from tkinter.messagebox import CANCEL


print("Welcome to the vending machine change maker program \nChange maker initialized.\nStock contains:")
print("    25 nickels\n    25 dimes\n    25 quarters\n    0 ones\n    0 fives")
# implement the logic for stock initial,prompt for a price till q
user = float(input("Enter the purchase price(xx.xx) or 'q' to quit: "))
while True:
    # check legal input , print input value
    while (round(user * 100, 2)) <= 0 or (round(user * 100, 2)) % 5 != 0:
        print("Illegal price: Must be a non-negative multiple of 5 cents.")
        user = abs(input("Enter the purchase price(xx.xx) or 'q' to quit: "))
    break
# menu of selections
print("Menu for deposits:\n  'n' - deposit a nickel\n  'd' - deposit a dime\n  'q' - deposit a quarter")
print("  'o' - deposit a one dollar bill\n  'f' - deposit a five dollar bill\n  'c' - cancel the purchase")
# deposit till full or c , amount remaining after each deposit
n = abs(0.05 * 100)
d = abs(0.1 * 100)
q = abs(0.25 * 100)
o = abs(1 * 100)
f = abs(5 * 100)
pp = abs(user * 100)
print("Payment due:", int(pp // 100), "dollars and ", int(pp % 100), "cents")
due1 = input("Indicate your deposit: ")
while True:
    nn = pp - n
    dd = pp - d
    qq = pp - q
    oo = pp - o
    ff = pp - f
    while due1 != 'n' and due1 != 'd' and due1 != 'q' and due1 != 'o' and due1 != 'f' and due1 != 'c':
        print("Illegal selection:", due1)
        due1 = input("Indicate your deposit: ")
        break
    while round(pp / 100, 2) > 1:
        if due1 == 'f':
            print("Payment due:", int(ff // 100), "dollars and", int(ff % 100), "cents")
        elif due1 == "o":
            print("Payment due:", int(oo // 100), "dollars and", int(oo % 100), "cents")
        elif due1 == 'q':
            print("Payment due:", int(qq // 100), "dollars and", int(qq % 100), "cents")
        elif due1 == 'd':
            print("Payment due:", int(dd // 100), "dollars and", int(dd % 100), "cents")
        elif due1 == 'n':
            print("Payment due:", int(nn // 100), "dollars and", int(nn % 100), "cents")
        elif due1 == 'c':
            CANCEL
        break
    while pp // 100 <= 1:
        if due1 == 'f':
            print("Payment due:", int(ff % 100), "cents")
            break
        elif due1 == 'o':
            print("Payment due:", int(oo % 100), "cents")
            break
        elif due1 == 'q':
            print("Payment due:", int(qq % 100), "cents")
            break
        elif due1 == 'd':
            print("Payment due:", int(dd % 100), "cents")
            break
        elif due1 == 'n':
            print("Payment due:", int(nn % 100), "cents")
            break
        elif due1 == 'c':
            CANCEL
    break
# update the stock
# calculate the change or refund
# number of coins to dispense and update the stock