1. Write a program that creates random addition questions (by generating random integer operands 
between -50 and 50) and asks the user to solve them. Your program should keep track of the number 
of good answers as well as of total questions asked. Variations: program asks ten questions then 
ends; another one that ends only when the user types "done". Either way the program should report 
a score at the end.

import random
user = 0
computer = 0

while True:
    n1=random.randrange(-50,50)
    n2=random.randrange(-50,50)
    answer = int(raw_input("What is " + str(n1) + "+" + str(n2)+ "?"))
    total = n1 + n2
    if answer == total:
        user += 1
        print "Good."
    else:
        computer += 1
        print "Bad."
    print "Score now is ", user, " - ", computer

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2. Write a program that randomly picks an integer between 0 and 100 and then asks the user 
to guess it. The game ends when the user guesses the number. Each time the user enters a guess 
feedback is provided (try higher, try lower) and a count is kept that records the number of 
incorrect guesses made up to that point. Report this number when the game ends. When you're
done, your task is to modify this program so that if the user makes 6 mistakes the user loses 
the game. 

import random
num = random.randrange(101)
guess = int(raw_input("I have a number 0-100. You get 6 guesses: "))
print num
count = 1
while guess != num and count < 6:
    if guess > num:
        print "Try lower. ",
    else:
        print "Try higher. ",
    guess = int(raw_input("Guess again: "))
    count += 1

if guess != num:
    print "You lose."
else:
    print "You win and it took you ", count, "guesses."

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3. Write a program that expects the user to enter a number per line and prints back (after 
every line) the current average of all the numbers entered up to that point. Program stops 
when the user enters the string "bye".

count = 0
sum = 0
line = raw_input("Enter: ")
while line != "bye":
    sum = sum + float(line)
    count = count + 1
    print sum / count
    line = raw_input("Enter: ")

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4. First, write an algorithm to settle the following question: A bank account starts 
out with $10,000. Interest is compounded at the end of every month at 6 percent per year 
(0.5 percent per month). At the beginning of every month, $500 is withdrawn to meet college 
expenses after the interest has been credited. After how many years is the account depleted? 
Now suppose the numbers ($10,000, 6 percent, $500) were user-selectable. Are there values 
for which the algorithm you developed would not terminate?

Here's the program that reads the three values and produces the correct answer: 


balance = float(raw_input("Initial balance: "))
interest = float(raw_input("Interest rate: ")) / 100 / 12
expenses = float(raw_input("Monthly withdrawal: "))

if interest * balance < expenses: 
    months = 0
    while balance + balance * interest - expenses >= 0:
        months = months + 1
        balance = balance + balance * interest - expenses
        print months, balance

    print months / 12, "years", months % 12, "months"
    print "Ending balance:", balance
else:
    print "You will never run out of money."

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5.  Strings have a split method that works like this: 

  >>> a = "this is a sentence" 
  >>> a.split() ['this', 'is', 'a', 'sentence'] 
  >>> 

Knowing this write a program that acts as a vending machine as illustrated below: 

a) you can enter names of coins, one per line or any number per line 
b) the program updates the balance as it recognizes the coins 
c) you can stop the program with "bye" (alone on a line) 

  Welcome to the Vending Machine! 
  coins> dime 
  Balance becomes: $0.10 
  coins> dollar dime dime 
  Balance becomes: $1.10 
  Balance becomes: $1.20 
  Balance becomes: $1.30 
  coins> quarter cent 
  Balance becomes: $1.55 
  Balance becomes: $1.56 
  coins> cent cent cent 
  Balance becomes: $1.57 
  Balance becomes: $1.58 
  Balance becomes: $1.59 
  coins> dime nickel dime dime nickel 
  Balance becomes: $1.69 
  Balance becomes: $1.74 
  Balance becomes: $1.84 
  Balance becomes: $1.94 
  Balance becomes: $1.99 
  coins> bye 
  Thanks for using this program. 

The program should report bad coins: 

  Welcome to the Vending Machine! 
  coins> dime dime mark dinar nickel ruble 
  Balance becomes: $0.10 
  Balance becomes: $0.20 
  I don't understand mark 
  Balance becomes: $0.20 
  I don't understand dinar 
  Balance becomes: $0.20 
  Balance becomes: $0.25 
  I don't understand ruble 
  Balance becomes: $0.25 
  coins> quarter 
  Balance becomes: $0.50 
  coins> shekel 
  I don't understand shekel 
  Balance becomes: $0.50 
  coins> bye 
  Thanks for using this program. 

The program should ignore empty lines:

  Welcome to the Vending Machine! 
  coins> 
  coins> 
  coins> 
  coins> 
  coins> dime 
  Balance becomes: $0.10 
  coins> 
  coins> 
  coins> dime 
  Balance becomes: $0.20 
  coins> nothing 
  I don't understand nothing 
  Balance becomes: $0.20 
  coins> bye 
  Thanks for using this program.

Here's the solution we worked out in class: 

print "Welcome to the Vending Machine!"

line = raw_input("enter> ")

balance = 0

while line != "done":
    coins = line.split()
    for coin in coins:
        if coin == "dime":
            balance += 10
        elif coin == "quarter":
            balance += 25
        elif coin == "nickel":
            balance += 5
        else:
            print "I don't understand", coin
        print "$" + str(balance / 100.0)
    line = raw_input("enter> ")

print "Thanks for using this program."

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6. Write a program that plays hangman with the user as described below. 

 >>> three 
      ----- 
  Guess a letter: h 
      -h--- 
  Guess a letter: x 
  Oops, this was your 1 th mistake! 
      -h--- 
  Guess a letter: x 
  I told you before, x is not in the secret word. 
      -h--- 
  Guess a letter: e 
      -h-ee 
  Guess a letter: a 
  Oops, this was your 2 th mistake! 
      -h-ee 
  Guess a letter: e
      -h-ee 
  Guess a letter: i 
  Oops, this was your 3 th mistake! 
      -h-ee 
  Guess a letter: r 
      -hree 
  Guess a letter: u 
  Oops, this was your 4 th mistake! 
      -hree 
  Guess a letter: t 
      three 
  Very good, you guessed the secret word! 
  >>> 

Here.s another session in which I lose:

  >>> two 
      --- 
  Guess a letter: a 
  Oops, this was your 1 th mistake! 
      --- 
  Guess a letter: e 
  Oops, this was your 2 th mistake! 
      --- 
  Guess a letter: i 
  Oops, this was your 3 th mistake! 
      --- 
  Guess a letter: o 
      --o 
  Guess a letter: u 
  Oops, this was your 4 th mistake! 
      --o
  Guess a letter: a 
  I told you before, a is not in the secret word. 
      --o 
  Guess a letter: o 
      --o 
  Guess a letter: m 
  Oops, this was your 5 th mistake! 
      --o 
  Guess a letter: n 
  Oops, this was your 6 th mistake! 
  Sorry, you lost the game, the secret word was: two 
  >>>

Here's the solution: 

import random

words = ("python", "exercise", "tangerine", "cloud", "water")

secret = words[random.randrange(len(words))]
print secret

print "Welcome to the game!"

dashes = "-" * len(secret)

while dashes != secret:
    guess = raw_input(dashes + ": ")
    if guess in secret:
        for index in range(len(secret)):
            if secret[index] == guess:
                # we'd like to write dashes[index] = guess but we can't, so we write
                dashes = dashes[0:index] + guess + dashes[index+1:] # this, to the same effect
    else:
        print "Nope."

print "You guessed the word, congratulations!"

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