CSC111 Lab 3 2015b

--D. Thiebaut (talk) 10:42, 20 September 2015 (EDT)

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The lab today deals with several concepts covered in Chapter 3 of Zelle. You have two programs to submit to Moodle, one for Challenge 1, and another one for Challenge 4. The deadline for the submission is Friday 9/25 at 11:55 p.m.
You should work on this lab with a programming-pair partner.

We are now moving to a more professional way of writing programs that always contain a main() function.

We are also changing the way you evaluate your programs on Moodle. Your program will be evaluated automatically when you submit it. If you want to make a change to the program, you will have to change it in IDLE first, then resubmit to Moodle. IDLE is a much better editor to edit code, and we want to reinforce good programming practice, and make sure you use IDLE, and not Moodle, to write programs!

Understanding how Floats take over Expressions

In this section I am asking you to play and get an understanding of important functions, and also how floating point numbers (numbers with a decimal point) take over expressions, when they are present in them.

Open the Python shell and type the expressions below. Try to predict the output of the interpreter when you are about to press the ENTER key.

>>> a = 3
>>> x = 1.5
>>> type( a )

>>> type( x )

>>> type( a * x )

>>> type( a * 100 )

>>> type( 1 )

>>> type( 1.0 )

>>> type( "1" )

>>> a / 3

>>> a // 3

>>> type( a/3 )

>>> type( 5/4 )

>>> type( 5//4 )

>>> type( int( 1.5 ) )

>>> int( 1.5 )

>>> round( 1.6 )

>>> round( 1.4 )

>>> round( -1.8 )

>>> type( round( 1.4 ) )

>>> round( -1.8 )

>>> abs( -4 )

>>> abs( 10 )

>>> type( abs( -19.3 ) )

>>> type( abs( -4 ) )

• Note how once something is a float, if forces whatever it gets combined with to yield a result that is float, except for the int() function, of course.

Challenge #0: (we always start at 0 in Computer Science!)

• Write a small program (either in the Python Shell, or in the Edit window), that asks the user to enter a number between 0 and 100, and that prints out 0 if the number is between 0 and 25 (25 not included), 1 if the number is between 25 and 50 (50 not included), 2 if the number is between 50 and 75 (75 not inclulded), and 3 if the number is between 75 and 100 (100 not included).

• Here is an example of the type of exchange I had with

>>> 
>>> x = eval( input( "Enter a number: " ) )
Enter a number: 75.7
>>> result =  ...  write an expression here that takes x and computes the expected result
>>> result
3
>>> x = 1
>>> result = ...  use the same expression you wrote above...
>>> result
0
>>> x = 24.99999
>>> result = ...  use the same expression you wrote above...
>>> result
0
>>> x = 25.00000001
>>> result = ...  use the same expression you wrote above...
>>> result
1
>>>

Teller Machine Program

This section will get you to write a program similar (though not necessarily the same) to the program we wrote in class on Monday. The program takes an integer (without a decimal part) amount of dollars and figures out how to break it down into the least number of 20-, 10-, 5-, and 1-bills.

Reviewing the Division Operators, // and %

Use the Python shell, and try to predict the result of the following operations.

>>> 21 // 5

>>> 21 % 5

>>> 9 // 2

>>> 9 % 2

>>> 13 // 3

>>> 13 % 3

>>> 139 // 20

>>> 139 % 20 

Beginning Program

• Write a program that contains
  • a short header with the program name (lab3.py, for example),
  • your name,
  • the date, and
  • A short description of the program.
• A main() function
• 3 different comment lines inside the main function, that will create an outline of your program.
• A call to main()

# lab3.py
# yourName 1
# yourName 2
# date
# A 1-paragraph description of what the program does.
#

def main():
     # get the initial amount

     # compute number of bills

     # output number of bills to give out

main()

• Save and Run the program, just to make sure you do not have a syntax error.

Define original amount

• Under the #get the initial amount comment, create a variable called amount and initialize it with a value of your choice. Pick a value that is not a multiple of 5.
• Add a print() statement under the #output number of bills comment, and make it print the amount the user wants to withdraw.
• Verify that your program works.

Compute the number of $20s to give out

• Using the right operator (//, /, or %), make your program compute the number of $20 and store that value in a new variable, called no20s. Add this code under the # compute number of bills.
• Make your program output the no20s variable in the output section.
• Verify that your program works.

Computing the Left-Over Amount

• Go back to the computation of the number of $20s, and compute the amount of money left over once the $20s are taken out of the amount. You have several ways of doing this. You can do it using the % modulo operator, or using multiplication and subtraction. Whichever method you use is fine for today.
• Make your program output the left-over amount, just to make sure that value is computed correctly.
• Verify that your program works fine.

Computing the Remaining Quantities

• Now that you have the structure for your program, add enough Python code to make your code display
  • The total amount
  • The number of $20-bills
  • The number of $10-bills
  • The number of $5-bills
  • The number of $1-bills

• Verify that your program works. Below is a typical output you should try to emulate:

Amount to withdraw =  97

Please lift keyboard and find: 
4 $20-bill(s)
1 $10-bill(s)
1 $5-bill(s)
2 $1-bill(s)

Flexibility and Adaptability

Imagine that your program will be used in an area where the bills do not come in 20, 10, 5 or 1 denominations, but in 100, 50, 10, and 1.

Figure out a way to make the least amount of change to your program so that it now outputs the correct break down for any amount, but in $100-, $50-, $10- and $1-bills.

Make sure your program works! Below is the output of the program if the amount is set to $97:

Amount to withdraw = $ 97

Please lift keyboard and find: 
0 $ 100 bill(s)
1 $ 50 bill(s)
4 $ 10 bill(s)
7 $ 1 bill(s)

Challenge #1: A Change Machine

• Using a similar approach, write a program that, given some number of pennies, will output the correct number of quarters, dimes, nickels, and pennies. You should initialize the amount of pennies with an integer, like this:

 pennies = 84

• Here is an example of what your program should output for 84 pennies:

Amount to withdraw = 84 cent(s)
Please lift keyboard and find: 
3 quarter(s)
0 dime(s)
1 nickel(s)
4 cent(s)

Moodle Submission

• Modify your program for Challenge 1, and rename it Lab3_1.py. It should now prompt the user for a number of pennies, and then, once it has received that number, it will print the number of coins that make up that quantity. We assume that the user may not be fully well behaved and might enter negative numbers, or numbers with a decimal point. For example, if the user enters -84, your program will treat this number as +84. If the user enters 84.5, your program will treat it as 84.
• Submit your program to the LAB 3 PB 1 section on Moodle. Note that the Moodle test program will strip all words from your output and will look only at the numbers, so you do not need to worry about the exact phrasing of your output.

When your program runs and the user inputs 84 (shown in magenta) it will look like below:

Enter an amount to withdraw: 84

Amount to withdraw = 84 cent(s) 
Please lift keyboard and find:  
3 quarter(s) 
0 dime(s) 
1 nickel(s) 
4 cent(s)

Formatted Output

Strings

In this section you will work on formatting strings, ints, and floats using the {...} formatting command.

• Try this statement out:

    name = "Snow White"
    print( "Hello {0:1}! How are you?".format( name ) )

• Then modify the {0:1} part and try these different combinations: {0:5}, {0:10}, {0:15}, {0:20}. For each one, make sure you understand why the output changes (or not).
• Then try these different formats: {0:>1}, {0:>5}, {0:>10}, {0:>15}, {0:>20}. Notice the right-justification of the string Snow White in this second set of outputs.

• Now try this piece of code:

    print( )
    for friend in [ "Bashful", "Doc", "Dopey",  "Happy", "Sleepy", "Sneezy", "Grumpy"]:
        print( "Hello {0:10}!".format( friend ) )

Printing 2 strings at once

• Change the print() statement so that you now print two different strings, each with its own {...} format:

    print( )
    for friend in [ "Bashful", "Doc", "Dopey",  "Happy", "Sleepy", "Sneezy", "Grumpy"]:
        print( "{0:1} wants to take {1:1} to the Valentine's ball." . format( friend, "Snow White" ) )

• Now switch the 0 and the 1 in the two {...} expressions, as illustrated in the line below:

        print( "{1:1} wants to take {0:1} to the Valentine's ball." . format( friend, "Snow White" ) )

• Notice how the first number in the {...} expressions is used to figure out which string to pick in the format(...) block.

Printing a String and an Int

• Try this formatting command:

    name = "Valentine's Day" 
    day = 15
    print( "{0:>20} is on the {1:1}th of the month" . format( name, day ) )
    name = "My birthday"
    day  = 6
    print( "{0:>20} is on the {1:1}th of the month" . format( name, day ) )

• Here's another statement to try:

    name = "Snow White"
    length = len( name )
    print( "the string {0:1} contains {1:1} characters" . format( name, length ) ) )

Printing Floats

• Copy/paste this block of code below in your program. Then run it. Verify that the output makes sense.

def main():
    print( "Printing PI" )
    pi = 3.14159
    print( "-------------------------" )
    print( "Pi={0:1.0f}!".format( pi ) )
    print( "Pi={0:2.0f}!".format( pi ) )
    print( "Pi={0:3.0f}!".format( pi ) )
    print( "Pi={0:4.0f}!".format( pi ) )
    print( "Pi={0:5.0f}!".format( pi ) )
    print( "Pi={0:6.0f}!".format( pi ) )
    print( "Pi={0:7.0f}!".format( pi ) )
    print( "Pi={0:8.0f}!".format( pi ) )
    print( "Pi={0:9.0f}!".format( pi ) )
    print( "-------------------------" )
    print( "Pi={0:9.1f}!".format( pi ) )
    print( "Pi={0:9.2f}!".format( pi ) )
    print( "Pi={0:9.3f}!".format( pi ) )
    print( "Pi={0:9.4f}!".format( pi ) )
    print( "Pi={0:9.5f}!".format( pi ) )
    print( "-------------------------" )
    print( "Pi={0:<9.1f}!".format( pi ) )
    print( "Pi={0:<9.2f}!".format( pi ) )
    print( "Pi={0:<9.3f}!".format( pi ) )
    print( "Pi={0:<9.4f}!".format( pi ) )
    print( "Pi={0:<9.5f}!".format( pi ) )

main()

Temperature Conversion

• Remember that we saw that a temperature in Celsius is computed as the temperature in Fahrenheit - 32, the difference multiplied by 5/9?
• Write a program with a main() function that contains a for-loop that displays two columns of numbers, the column on the left showing degrees Fahrenheit, and the column on the right showing Celsius.

• Your program should prompt the user for the beginning and end temperatures in Fahrenheit, and display 2 columns of numbers.

Starting temperature? 20
Ending temperature? 40

20 -6.666666666666667
21 -6.111111111111111
22 -5.555555555555555
23 -5.0
24 -4.444444444444445
25 -3.888888888888889
26 -3.3333333333333335
27 -2.7777777777777777
28 -2.2222222222222223
29 -1.6666666666666667
30 -1.1111111111111112
31 -0.5555555555555556
32 0.0
33 0.5555555555555556
34 1.1111111111111112
35 1.6666666666666667
36 2.2222222222222223
37 2.7777777777777777
38 3.3333333333333335
39 3.888888888888889
40 4.444444444444445

Challenge #3:

• Use the {...} formatting command to make your output look nicer:

Starting temperature? 20
Ending temperature? 40
 
20       -6.67
21       -6.11
22       -5.56
23       -5.00
24       -4.44
25       -3.89
26       -3.33
27       -2.78
28       -2.22
29       -1.67
30       -1.11
31       -0.56
32        0.00
33        0.56
34        1.11
35        1.67
36        2.22
37        2.78
38        3.33
39        3.89
40        4.44

(Note the blank line between the input section, and the output of the program. You need your program to output it!)

Moodle Submission

• Make sure your program is called Lab3_3.py and submit it to Moodle, to the LAB 3 PB 3 section. Note that your output must match exactly the one shown above, with the right number of spaces, the same number of decimals, and the same number of lines. Your program must use a loop to generate the output, and must use formatting {...} commands.

Accumulating Quantities

The idea for this section is that some quantities can be computed not all at once, but instead, one piece at a time. Computers are extremely fast and ready for this type of accumulation of data. In this section we look at several ways to do this with various types of data. We will see later on in the semester, that some of the operations we are performing here can be done more easily some other way. That's ok. Programming is also the art of solving problems, and not necessarily to find the most elegant or fastest solutions (although it is good to be aware of them!)

Sum of a list of numbers

• Add this piece of code to your program (or create a new program):

    sumAll = 0
    for n in [100, -50, -20, -10, 15, 5 ]:
        sumAll = sumAll + n

    print( "sum = ", sumAll )

• Run the code. Add the numbers by hand to make sure your program outputs the correct information.
• Add this print statement inside the for-loop, right after the "sumAll = ..." statement:

         print( "n = {0:3} sum = {1:3}" . format( n, sumAll ) )

• Run your code. Observe how the loop allows the variable sumAll to grow with the addition of every new number in the list.

Note that the rule for accumulating quantities with a loop is always the same:

1. first you initialize a variable to represent some null quantity
2. then you loop, and in the loop you increase the variable with a new quantity given by the loop.
3. at the end of the loop, your variable will contain an accumulation of all the values your loop touched, or created.

Challenge #5:

• Replace the list of numbers [100, 10, -30, -2, 20, 5 ] by the range() function and make your program compute the sum of all the even numbers between 0 and 100, included.
• Verify that your program outputs 2550 as the result! You do not need to make your program output all the intermediate values of sumAll.

Count the Items in a List

• Try this piece of code now:

count = 0
for n in [ 100, 10, -30, -2, 20, 5 ]:
        count = count + 1

print( "there are", count, "items in the list" )

• See how this code is different from the loop in the previous section. Here we add 1 to the counter every time we go through the loop. In other words, we add 1 for every item we find in the list. So, in effect, we are counting the items in the list.
• Run your code and see what it outputs.
• Add print statement inside the loop, below the count = count + 1 line, and make the print statement print n and count. Don't worry about the formatting.
• Run your code. Do you see the program counting the items it finds in the list of numbers?

Challenge #6:

• Write a program that uses a for-loop that scans a list of numbers: [1, 2, 2, 1, 2, 3, 3, 2, 1, 0]
• Make your program compute the average of the numbers in the list. The average is the sum of all numbers divided by the number of items.
• Your program should output the average at the end, as a floating-point number.
• Run your program. Verify that you get the correct result (sum = 17 average = 1.70).

Accumulating Strings

• Here's a new program to try:

    line = ""
    for friend in [ "Bashful", "Doc", "Dopey", "Happy", "Sleepy", "Sneezy", "Grumpy" ]:
        line = line + friend + ", "

    print( "line =", line )

Challenge #7: (Challenging!)

• Write a program that contains a single loop, of the form for n in [ 2, 3, 5, 3, 2 ]:, and that accumulates a string, which, when it is fully computed, is equal to "**---*****---**".

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Solution Program

# lab3Solutions.py
# D. Thiebaut
# Solution programs for CSC111 Lab #3
#
# All the solutions are group into one large main program.

def main():

    # Challenge 0
    for x in [ 0, 1, 24.99, 25, 25.001, 30, 51, 79, 99]:
        result = int( x/25 )
        print( "x = ", x, " result = ", result )

    # Teller Machine
    # Takes some amount of $ and breaks it down in 20, 10, 5, and 1
    # dollar bills.

    # set the amount
    amount = 97

    # break it down
    no20s    = amount // 20
    leftOver = amount % 20
    no10s    = leftOver // 10
    leftOver = leftOver % 10
    no5s     = leftOver // 5
    leftOver = leftOver % 5
    no1s     = leftOver

    # printout the number of bills
    print()
    print( "You want to withdraw ${0:1}".format( amount) )
    print( "Lift the keyboard and find:" )
    print( "{0:4} $20-bill(s)". format( no20s ) )
    print( "{0:4} $10-bill(s)". format( no10s ) )
    print( "{0:4} $5-bill(s)". format( no5s ) )
    print( "{0:4} $1-bill(s)". format( no1s ) )


    # ==========================================================
    # Teller Machine with a different set of denominations
    # set the amount
    amount = 197

    # break it down
    no100s   = amount // 100
    leftOver = amount % 100
    no50s    = leftOver // 50
    leftOver = leftOver % 50
    no10s    = leftOver // 10
    leftOver = leftOver % 10
    no1s     = leftOver

    # printout the number of bills
    print()
    print( "You want to withdraw ${0:1}".format( amount) )
    print( "Lift the keyboard and find:" )
    print( "{0:4} $100-bill(s)". format( no20s ) )
    print( "{0:4} $50-bill(s)". format( no10s ) )
    print( "{0:4} $10-bill(s)". format( no5s ) )
    print( "{0:4} $1-bill(s)". format( no1s ) )

    # simple output
    print()
    name = "Snow White"
    print( "Hello {0:1}! How are you?".format( name ) )
    print( "Hello {0:5}! How are you?".format( name ) )
    print( "Hello {0:10}! How are you?".format( name ) )
    print( "Hello {0:15}! How are you?".format( name ) )
    print( "Hello {0:20}! How are you?".format( name ) )

    print( "Hello {0:>1}! How are you?".format( name ) )
    print( "Hello {0:>5}! How are you?".format( name ) )
    print( "Hello {0:>10}! How are you?".format( name ) )
    print( "Hello {0:>15}! How are you?".format( name ) )
    print( "Hello {0:>20}! How are you?".format( name ) )
    
    # Formatted output, Version 1
    print( )
    for friend in [ "Bashful", "Doc", "Dopey",
                "Happy", "Sleepy", "Sneezy", "Grumpy"]:
        print( "Hello {0:10}!".format( friend ) )

    # Swapping first and second strings
    print( )
    for friend in [ "Bashful", "Doc", "Dopey", "Happy", "Sleepy", "Sneezy", "Grumpy"]:
        print( "{1:1} wants to take {0:1} to the Valentine's ball."
           . format( friend, "Snow White" ) )

    for friend in [ "Bashful", "Doc", "Dopey", "Happy", "Sleepy", "Sneezy", "Grumpy"]:
        print( "{0:1} wants to take {1:1} to the Valentine's ball."
           . format( friend, "Snow White" ) )

    # Unformatted dwarf names and length of names
    for friend in [ "Bashful", "Doc", "Dopey",
                "Happy", "Sleepy", "Sneezy", "Grumpy"]:
        print( friend, len(friend) )
   
    # Formatted output, Version 2
    bar = "+-" + 10*'-' + "-+-" + 3*'-' + "-+" 
    print( bar )
    for friend in [ "Bashful", "Doc", "Dopey",
                "Happy", "Sleepy", "Sneezy", "Grumpy"]:
        print( "| {0:10} | {1:3} |".format( friend, len(friend) ) )
    print( bar )

    # print string and int
    name = "Valentine's Day" 
    day = 15
    print( "{0:>20} is on the {1:1}th of the month" . format( name, day ) )
    name = "My birthday"
    day  = 6
    print( "{0:>20} is on the {1:1}th of the month" . format( name, day ) )

    # printing floats
    print()
    print( "Printing PI" )
    pi = 3.14159
    print( "Pi={0:1.0f}!".format( pi ) )
    print( "Pi={0:2.0f}!".format( pi ) )
    print( "Pi={0:3.0f}!".format( pi ) )
    print( "Pi={0:4.0f}!".format( pi ) )
    print( "Pi={0:5.0f}!".format( pi ) )
    print( "Pi={0:6.0f}!".format( pi ) )
    print( "Pi={0:7.0f}!".format( pi ) )
    print( "Pi={0:8.0f}!".format( pi ) )
    print( "Pi={0:9.0f}!".format( pi ) )
    print( "-------------------------" )
    print( "Pi={0:9.1f}!".format( pi ) )
    print( "Pi={0:9.2f}!".format( pi ) )
    print( "Pi={0:9.3f}!".format( pi ) )
    print( "Pi={0:9.4f}!".format( pi ) )
    print( "Pi={0:9.5f}!".format( pi ) )
    print( "-------------------------" )
    print( "Pi={0:<9.1f}!".format( pi ) )
    print( "Pi={0:<9.2f}!".format( pi ) )
    print( "Pi={0:<9.3f}!".format( pi ) )
    print( "Pi={0:<9.4f}!".format( pi ) )
    print( "Pi={0:<9.5f}!".format( pi ) )
    
    
    # Print table of temperatures
    print()
    for Fahr in range( 20, 41, 2 ):
        print( Fahr, (Fahr-32.0)*5.0/9 )
        
    print()
    for Fahr in range( 20, 41, 2 ):
        print( "{0:10.2f}F = {1:10.2f}C".format( Fahr*1.0, (Fahr-32.0)*5.0/9 ) )


    # Print table of temperatures with bars around
    bar = "+-" + 10*'-'  + "--+-" + 10*'-' + "--+"
    print( bar )
    print( "| {0:>10}  | {1:>10}  |".format( "Fahrenheit", "Celsius" ) )
    print( bar )
    for Fahr in range( 20, 41, 2 ):
        print( "| {0:10.2f}F | {1:10.2f}C |".format( Fahr*1.0, (Fahr-32.0)*5.0/9 ) )
    print( bar )

def main2():
    # compute the sum a list of numbers
    # (note that there's a much simpler way to do this in Python, which
    # we'll see later during the semester.)
    print()
    sumAll = 0
    for n in [100, 10, -30, -2, 20, 5 ]:
        sumAll = sumAll + n
        print( "n = {0:3} sum = {1:3}" . format( n, sumAll ) )
    print( "sum = ", sumAll )

    # add-up the even numbers between 0 and 100.
    print()
    sumAll = 0
    for n in range( 0, 101, 2 ):
        sumAll = sumAll + n
    print( "the sum of all the even numbers from 0 to 100, included, is",
           sumAll )
    
    # count how many items are in the list
    print()
    count = 0
    for n in [ 100, 10, -30, -2, 20, 5 ]:
        count = count + 1
        print( "n = {0:3} count = {1:3}" . format( n, count ) )
    print( "there are", count, "items in the list" )
    

    # compute the sum and average of a list of numbers
    print()
    sumAll = 0
    count = 0
    for n in [1, 2, 2, 1, 2, 3, 3, 2, 1, 0]:
        sumAll = sumAll + n
        count = count + 1
        
    print( "sum = {0:1}  average = {1:1.2f}" . format( sumAll, sumAll*1.0/count ) )

    # compute the factorial of a number
    # factorial( 10 ) = 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1
    print()
    n = 20
    fact = 1
    for i in range( 1, n+1 ):
        print( "computing fact * i = {0:1} * {1:1} = {2:1}"
               .format( fact, i, fact*i ) )
        fact = fact * i
    print( "factorial({0:1}) = {1:1}".format( n, fact ) )

    # create a string with all the names of the 7 dwarves
    print()
    line = ""
    for friend in [ "Bashful", "Doc", "Dopey", "Happy", "Sleepy", "Sneezy", "Grumpy"]:
        line = line + friend + ", "

    print( "line =", line )

    # Challenge
    print()
    line = ""
    char1 = "*"
    char2 = "-"
    for n in ( 2, 3, 5, 3, 2 ):
        line = line + n*char1
        char1, char2 = char2, char1

    print( "line = ", line )
main2()

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