COS 100: Introduction to Programming

Fall 2019

Lab 8: Working with strings

In-class practice labs will not directly impact your grade (although you'll get your standard participation point for staying on task), and will serve to help you with homework projects.

Lab 8A: Wrapping long lines

• Goal: Practice with strings (and functions).
• Prompt the user for an integer for width.
• Prompt the user for a sentence (which may or may not include spaces).
• Loop through and print the sentence wrapped so every line (except the last) has width as the user requested.
• Continue to use functions properly. (Which task(s) should you leave in the main function? Which task(s) should you put in a separate function? What should you name that function? Even though there are a lot of different ways to do this, there is more or less just one preferred way to organize your code. Discuss with your neighbours before you start coding.)
• Sample run:

  Width: 4
  Sentence: Computer Science is pretty fun!
  Comp
  uter
   Sci
  ence
   is
  pret
  ty f
  un!
  

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Lab 8B: Counting letters

• Goal: Help you get started with a later homework project (yes, really). Make sure you save a copy of your work so you can use it later.
• Write a function that takes in two strings as input, the first is some text and the second is a single letter of the alphabet, and returns a count of how many times that letter shows up in the text.
• For example, the string "Introduction to Programming" contains three 'n' characters. So a call to count_char("Introduction to Programming", "n") should return the integer 3.
• Python strings are smart and know how to count:

  text = "Introduction to Programming"
  letter = "n"
  print(text.count(letter))
  

  will print 3. Do not use this built-in method right now. The point of this lab is to get some practice by writing your own version (using loops, of course).

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Challenge Lab 8C: Counting substrings

• Make a copy of your 8B code (you'll want to use the original version for a later homework project) and change it as follows.
• Instead of taking in a text and a letter, take in two strings haystack and needle.
• Count the number of times needle is found in haystack.
• If needle is a single character, your new function behaves exactly like the old one.
• If your haystack is "How much wood would a woodchuck chuck if a woodchuck could chuck wood?" and needle is "wood" then your function should return 4.
• How many times does the needle "HaHa" occur in the haystack "HaHaHaHaHa"? One could argue that there are 4 overlapping occurrences. Or one could argue that there are only 2 non-overlapping occurrences. Python's built-in "HaHaHaHaHa".count("HaHa") returns 2. You should try to write your function in two ways, one that returns 2 and one that returns 4. (Do the one you think is easier first, then modify it to make the other version later.)