reveal.js

# Strings

---

CS 65 // 2021-03-09

## 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) (3/10) at 7pm

## 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

# CS 65 Tutoring

# Questions
## ...about anything?

# Loops Lab: Debrief

# Strings

## The `str` Type
- **Purpose**:
    + To manipulate "text" (sequences of characters)
- **Express:**
    + Strings are written: `"abc"` or `'abc'`
- **Operations:**
    + `s1 + s2`: concatenates two strings together
    + `s * num`: concatenates `num` copies of `s` together

## The `str` Type
- **Other Operations**:
    + `len(s)`: gets the **length** of the string `s`
    + 
 `s[index]`: gets the character at the given index
    + 
 `s[start:end]`: gets the substring that starts at index `start` and ends before index `end`
    + 
 `s.upper()`: gets a copy of `s` where each lowercase character is replaced by its uppercase
    + 
 `s.lower()`: gets a copy of `s` where each uppercase character is replaced by its lowercase
    + 
 `s1 in s2`: returns true if `s1` is a substring of `s2`

## Unicode
- Unicode is an **international standard** for encoding characters
- 
 In particular, every character is given an associated number called an **ordinal**
- 
 In Python, you can turn a character into its ordinal number using the `ord(ch)` function
- 
 You can also turn numbers into their associated character using the `chr(ch)` function

## Mutability / Immutability
- Many basic values in Python are **immutable**, i.e., they cannot be changed after they are created
    + 
 `int`s, `float`s, and `str`s are all immutable
    + 
 Thus, expressions `s[2:7]` constructs a **new string** rather than modifying `s`
- 
 Graphics objects are **mutable**---commands such as `rect.move(50,0)` mutate the object rather than create a new rectangle

## Traversal with a `while` Loop
- We can iterate over string using a while loop such as:
    ```py
    fruit = "banana"
    index = 0
    while index < len(fruit):
        letter = fruit[index]
        print(letter)
        index = index + 1
    ```

## Tranversal with a `for` Loop
- We can also use a `for` loop to traverse a list
    ```py
    fruit = "banana"
    for letter in fruit:
        print(letter)
    ```

# Self Checks

# Lab Time