reveal.js

# String Processing

---

CS 65 // 2021-03-11

## Extra Credit Activities
- [Study Abroad 101 Info Session](https://calendar.drake.edu/event/study_abroad_101_info_session?utm_source=newsletter&utm_medium=email&utm_content=DETAILS&utm_campaign=Faculty-March-9#.YEe9CxBKh7M)
    + Friday, March 12 from 10:00am to 10:30am
    + Virtual Event

## Extra Credit Activities
- [The Anderson Gallery](https://linktr.ee/theandersongallery)
    + 50th Annual Juried Student Exhibition
    + [Virtual Opening and Awards Ceremony](https://www.youtube.com/watch?v=yvlpDFYudVg)
    + [Virtual Performance and Lecture](https://www.youtube.com/channel/UCPCCKI0rPk97vpY61BvCK9w/videos)

## Extra Credit Activities
- MathCS Special Interest Group
    + Microsoft Team to help foster community between the students and faculty interested in topics related to Mathematics and Computer Science

# Exam 2

## Exam 2
- Exam 2 is going to be released...later tonight
- Be sure to carefully read the [exam procedures]( ../../resources/exam-procedures.html) before starting the exam
- 
 It is an **individual**, take-home exam
    + 
 No discussing with peers, mentors, or tutors
    + 
 You may only discuss the exam with me

## Tips for the Exam
- Program little by little, saving often, and getting one piece to work at a time
- 
 Ask for help!
    + Come talk to me if you're stuck for a while
- 
 Test your programs on a variety of inputs
- 
 Start early

# String Exercises

## Exercise 1
- Write a function `lowercase(s)` that takes a string as a parameter and returns a copy of `s` except each uppercase character is replaced with a lowercase one.
- 
 Now write `uppercase(s)`.

## Exercise 2
- Write a function called `substring(s, start, end)` that returns `s[start:end]`---but without using Python's built-in string slicing notation

# Files

## Reading from a File
- It is possible to read input **from a file** rather than directly from the user using `input(..)`
- 
 You can **open** a file for reading by calling
    ```py
    f = open("path/to/file", "r")
    ```
+ 
 The `"r"` opens the file for **reading** and the path is relative to the directory of your program

## Reading from a File
- Once a file is open, you can **read** text from it using the following methods

```py
f = open("my_file.txt", "r")
f.read()      # Returns the ENTIRE file as a long string
f.read(n)     # Returns the next n characters as a string
f.readline()  # Returns the next LINE as a string
```

## Looping Over a File
- A file can be considered a sequence of **lines** separated by newline characters `"\n"`
- Therefore, we can loop over a file just like any other sequence:
    ```py
    my_file = open("my_file.txt", "r")
    for line in my_file:
        print(line)
    ```

## Looping Over a File
- This `for`-loop notation is shorthand for:
    ```py
    my_file = open("my_file.txt", "r")
    line = my_file.readline()
    while line != "":
        print(line)
        line = my_file.readline()
    ```

# Exercises

## Exercise 1
- Write a program that reads `words.txt` and prints only the words with more than 20 characters (not counting whitespace).

## Exercise 2
- Write a function called `has_no_e` that returns `True` if the given word doesn’t have the letter `"e"` in it.
- 
 Write a program that reads `words.txt` and prints only the words that have no `"e"`.
- 
 Compute the percentage of words in the list that have no `"e"`.

## Exercise 3
- Write a function named `avoids` that takes a word and a string of forbidden letters, and that returns `True` if the word doesn’t use any of the forbidden letters.
- 
 Write a program that prompts the user to enter a string of forbidden letters and then prints the number of words that don’t contain any of them.

## Exercise 4
- Write a program that reads `words.txt` and prints the **longest word** in the list of words

## Exercise 5
- Write a function called `count_vowels` that returns the number of vowels in a string.
- Write a program that reads `words.txt` and prints the word that contains the most vowels.

# Looping with Indices

## Looping with Indices
- In these previous examples, it was possible to iterate over the strings using a `for` loop such as
    ```py
    for ch in s:
        print(ch)
    ```
- 
 This can also be written in the following way:
    ```py
    for i in range(len(s)):   # Loops over indices of s
        print(s[i])           # s[i] is the current character
    ```

## Exercise 6
- Write a function called `is_abecedarian` that returns `True` if the letters in a word appear in alphabetical order (double letters are ok).
- How many abecedarian words are there in `words.txt`?

# Other Exercises