CSC111 Lab 8 2015

--D. Thiebaut (talk) 14:10, 22 March 2015 (EDT)

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Part 1: While Loops

Exercise 1: Robust Input with While

def getPositiveNumber():
    #
    # put your code here
    #
    return 10   # just to make sure the code is accepted by Idle


def main():

    # Part 1, Exercise 1
    x = getPositiveNumber()
    print( "getPositiveNumber() returned", x )

main()

Complete the function getPositiveNumber() so that it asks the user for a number larger than 0, and keeps on prompting the user as long as she doesn't enter a valid number.

Below is an example of the interaction between computer and user.

Please enter a number greater than 0: -1
-1 is invalid.
Please enter a number greater than 0: -3
-3 is invalid.
Please enter a number greater than 0: 0
0 is invalid.
Please enter a number greater than 0: 20
getPositiveNumber() returned 20
>>>

Exercise 2: Ask for Yes/No answer

Same idea as in Exercise 1, but this time the new function, called getYesNo() will keep on asking a question until the user's input is "YES", "yes", "y", "NO", "no", or "n". Any combination of lower/upper case in the spelling is accepted ("yES" is valid).

Source

def getYesNo():
    #
    # put your code here
    #
    return "Y"    # just to make sure the code works as is.
            
def main():
    # Part1, Exercise 2
    likesChoco = getYesNo()
    if likesChoco in ["YES", "Y" ]:
        print( "Me too!" )
    else:
        print( "Sorry to hear that!" )
        
main()

Example output

Do you like chocolate (Y/N)? possibly
please enter by 'Yes' or 'No'

Do you like chocolate (Y/N)? I don't know
please enter by 'Yes' or 'No'

Do you like chocolate (Y/N)? Oui
please enter by 'Yes' or 'No'

Do you like chocolate (Y/N)? y
Me too!

Exercise 3: While Loop and Reading File

# createFile: creates a text file containing a haiku followed by the line <<<END>>>
# followed by some text about the source of the haiku and the rights of use.
def createFile( fileName ):

    # open the file
    file = open( fileName, "w" )

    # write some text
    file.write("""
    An old pond!
    A frog jumps in-
    The sound of water.
    <<<END>>>
    Haikus from http://www.toyomasu.com/haiku/
    Feel free to use anything from this page as
    long as you make references and links to HAIKU
    for PEOPLE. Last updated: Jan 10th. 2001.
    Edited by Kei Grieg Toyomasu,
    kei at toyomasu dot com""" )

    # close the file
    file.close()

def readFileTillMarker( fileName ):
    #
    # add your code here
    #
    return []   # just to make sure the code compiles. 

def main():
    # Part 1, Exercise 3
    # create a sample text file for testing.  The file will contain the string <<<END>>>
    # in it.
    createFile( "lab8Demo.txt" )

    # get all the lines before but not including <<<END>>>
    lines = readFileTillMarker( "lab8Demo.txt" )

    # display the lines returned.  We strip them to remove the extra \n at the end and
    # the extra spaces at the front of each line.
    print( "Lines found by readFileTillMarker(): " )
    for line in lines:
        print( line.strip() )
        
main()

Same idea as the previous 2 exercises. This time you need to add code to the function readFileTillMarker() so that it will read all the lines contained in the file whose name is passed as a parameter, and that appear before the marker string <<<END>>>. In other words, the function reads the lines, adds them to a list of lines, until it finds a line containing the string <<<END>>>. It returns a list of all the lines read.

The function createFile() creates a simple file you can use for testing. Take a look at it to make sure you understand the format of the data.

Here's an example of how your program should work.

Lines found by readFileTillMarker(): 

An old pond!
A frog jumps in-
The sound of water.

Exercise 4: A bit of mathematics

Pi can be computed by adding the following terms (http://en.wikipedia.org/wiki/Pi):

Here's a program that shows how the variable sum, where we accumulate the terms, gets closer and closer to PI:

def computePi():
    sum = 0
    multiplier = 1
    
    for i in range( 1, 20, 2 ):
        sum = sum + multiplier * 4.0 / i
        multiplier = -multiplier
        print( "Pi = ", sum )

Modify this program so that it stops when the first 3 digits of sum are equal to 3.14. In other words you need to change the loop to a while loop, and make it stop when the sum is a number of the form 3.14xxxxxxx.

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