CSC111 Lab 4 Solutions 2014

--D. Thiebaut (talk) 20:31, 19 February 2014 (EST)

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Solution Programs

# Solutions for Lab 4
# D. Thiebaut

# ===========================================================
# Exercise 1
print( "\n========================\nExercise 1\n========================" )

x = int( input( "enter an integer less than 3 or greater than 9: " ) )
while  3 <= x <= 9: 
   print( "invalid input!" )
   x = int( input( "enter an integer less tan 3 or greater than 9: " ) )

print( "x = ", x )

# ===========================================================
# challenge 1
print( "\n========================\nChallenge 1\n========================" )
x = int( input( "enter an integer between 3 and 9: " ) )
while   not (3 <= x <= 9 ):
   print( "invalid input!" )
   x = int( input( "enter an integer between 3 and 9: " ))

print( "x = ", x )

# ===========================================================
# Exercise 2
print( "\n========================\nExercise 2\n========================" )

#--- ask user question ---
answer = input( "Do you like chocolate (Y/N)? " )
answer = answer.lower().strip()

#--- keep on asking while invalid ---
while answer != 'y' and answer != 'yes' and answer != 'n' and answer != 'no':
    answer = input( "Please reenter: " )
    answer = answer.lower().strip()

#--- now that we know the answer, give feedback ---
if answer == 'n' or answer == 'no' :
    print( "That's terrible" )
else:
    print( "That's great!" )

# ===========================================================
# Exercise 3
print( "\n========================\nExercise 3\n========================" )

human = input( "what is your play (R, S, P)? " )
human = human.strip().lower()
while human != 'p' and human != 's' and human != 'r':
    human = input( "I didn't get that.  Please reenter: " )

print( "You have played", human.upper() )

# ===========================================================
# Challenge 2
# buggy program that is supposed to compute
# the sum of even numbers and stop as soon as
# the sum is greater than or equal to 20.  Your
# job is to fix the program using PythonTutor.

print( "\n========================\nChallenge 2\n========================" )

# solution 1
sum = 0
num = 0

while sum < 20:
    num = num + 2       # <--- fix by switching statements
    sum = sum + num

print( "the sum of the even numbers from 0 to %d is %d\n"
       % ( num, sum ) )

# solution 2
sum = 0
num = 0

while sum < 20:
    sum = sum + num
    num = num + 2    

# num is always 2 larger that the associated sum
# decrease num to undo the last increment statement in the loop
num = num - 2 
print( "the sum of the even numbers from 0 to %d is %d\n"
       % ( num, sum ) )

# ===========================================================
# Exercise 5
print( "\n========================\nExercise 5\n========================" )

initBalance = 1000.00
intRate = 0.05

print( "initial balance = $%1.2f" % initBalance )

newBalance = initBalance
period     = 0
while period < 4:
    newBalance = newBalance + newBalance * intRate
    period = period + 1
    print( "after Investment Period %d, new balance = $%1.2f"
           % ( period, newBalance ) )



# ===========================================================
# Challenge 3
print( "\n========================\nChallenge 3\n========================" )

initBalance = 1000.00
intRate = 0.05

print( "initial balance = $%1.2f" % initBalance )

newBalance = initBalance
period     = 0

targetBalance = float( input( "What is your target balance? " ) )

while newBalance < targetBalance:
    newBalance = newBalance + newBalance * intRate
    period = period + 1
    if period == 1:
        plural = ""
    else:
        plural = "s"
    print( "after %2d investment period%s, balance = $%6.2f"
           % ( period, plural, newBalance ) )

# ===========================================================
# Challenge 4-5
print( "\n========================\nChallenge 4-5\n========================" )

print( "please enter positive integers at the prompt.  Enter -1 to stop" )

sum   = 0
x     = 0
count = 0
while x != -1 and sum < 20:
    x = int( input( "Enter a positive integer (-1 to stop): " ) )
    if x != -1:
        sum = sum + x
        count = count + 1

print( "The sum of the %d number(s) you have entered is %d" % ( count, sum ) )