Free Recall

• Get out a sheet of paper or open a text editor
• For 2 minutes write down whatever comes to mind about the last class
  • This could be topics you learned
  • Questions you had
  • Connections you made

Setting Up CS Circles

• Sign up for a free account on CS Circles
• This is mandatory
• Next set jhaugh as your “guru”
  • Click “Edit my profile” in the top right menu
  • Set the guru field to jhaugh
• I will now be able to see your progress and give you credit in Canvas

Coding Exercise: Bonjour

• Now take a few minutes to read chapter 0
• Then complete Coding Exercise: Bonjour
• I will give you about 10 minutes to do this

Assignment Statement

• An assignment statement is an operation which creates or modifies a variable
• It takes the following form: name = value
• For example: abc = 123
  • Creates a variable named abc containing the value 123

Variables

• Variables are used to store data the program needs
• They need to have an initial value
• They can change over time

Variable Example

x = 5
print(x)
x = 6
print(x)

Visualize

Variables Can Depend On Other Variables

What will the following code print?

x = 5
y = x + 1
print(x)
print(y)

Visualize

Variables Can Depend On Other Variables

What will the following code print?

x = 5
y = x + 1
x = 6
print(x)
print(y)

Visualize

Code Is Executed Top To Bottom

x = 5
y = x + 1
x = 6
print(x)
print(y)

6
6

Key Idea: Each line of code effects lines of code after it

Try It: Three Variables

What does the following code print? Try it by hand first.

a = 9
b = a * 3
a = 10
c = a + b
print(a)
print(b)
print(c)

Visualize

Try It: Three Variables

a = 9
b = a * 3
a = 10
c = a + b
print(a)
print(b)
print(c)

10
27
37

Terminology: Statements vs Expressions

• We have seen several mathematical expressions so far
  • 9
  • a * 3
  • a + b
• We have only seen the assignment statement so far (we will see many more soon)
  • a = 9
  • b = a * 3
  • c = a + b
• Expressions are units of code which always have a value
• Statements are units of code that effect the state of the code (illustrated in the table on the previous) but have no value

Other Values

• Variables can save more than just numbers
• Variables can hold any value
• Some other types of values we will see in this class:
  • Strings
  • Floats
  • Lists

Strings

• Strings are a sequence of characters
• Creation of strings takes one of two forms:
  • Single Quotes (’)
  • Double Quotes (“)
• You must end the string with the same quote type you started it with
• For example, both of the following are valid in Python:
  • 'Hello world'
  • "Hello world"
• However, the following are invalid:
  • 'Hello world"
  • "Hello world'
• You must be consistent

String Variable

As stated before variables can hold strings:

msg = "mon ami"
print(msg)

Visualize