#AP Computer Science Principles: Variables and Data Types - Your Last-Minute Guide 🚀

Hey! Let's get you ready to ace this exam. We're going to break down variables and data types so everything is crystal clear. Think of this as your cheat sheet for tonight!

#Variables: The Heart of Your Program

#What is a Variable?

• A variable is like a container that holds a value. It's a named storage location in the computer's memory. Think of it like a box with a label on it. 📦
• You use variables to store and manipulate data in your programs.
• They are represented by names (usually letters or words).

#Assignment and Reassignment

• Assignment: Giving a variable a value for the first time. In pseudocode, we use ←. In Python, we use =.
• Reassignment: Changing the value of a variable. The variable will always hold the most recent value assigned to it.

# Example in Python
number = 7  # Assignment
changed_number = number # changed_number is now 7
number = 17 # Reassignment
print (changed_number) # Output: 7

• Use extra print statements to check values during execution.
• Hand tracing can help reduce uncertainty (remember Big Idea 1!).

#Data Types: What Kind of Data Is It?

#What are Data Types?

• Data types are categories that classify the type of value a variable can hold. 🗂️
• Common data types include integers, floats, strings, lists (arrays), and booleans.
• The data type determines what operations you can perform on the data.

#Numerical Data

• Integers (int): Whole numbers (positive or negative). Example: 5, -10, 0.
• Floats (float): Numbers with decimal points. Example: 3.14, -2.5, 0.0.

python
int_example = 5
float_example = 5.52

#Strings

• Strings (str): Sequences of characters, enclosed in quotation marks.
• Can be letters, words, numbers, or symbols. Example: "Hello"
• Use single or double quotes.

python
string_example = "Hello, World!"

#Booleans

• Booleans (bool): Represents truth values: True or False.
• Used for conditional logic and decision-making.

python
bool_example = True

#Lists (Arrays)

• Lists (list): Ordered collections of items. Can contain elements of different data types.
• Enclosed in square brackets [].

python
list_example = [1, 2, "three", 4.0]

• Variables are named storage locations.
• Data types classify the kind of values variables can hold.
• Common data types: int, float, str, bool, list.

python
x = 5
x = x + 2

a) 5
b) 2
c) 7
d) Error

#

• Go through the practice questions again. You got this!

$$e^{i \pi}-1=0$$

$$E=mc^2$$