🎉 Welcome Back, Programmer! 🎉

Session 4: Variables and Data Types

Ready to teach computers to remember? 🧠

Today we learn how to store information in our programs!

✨ Let's give our programs memory! ✨

📝 Structure & Syntax Homework Review! 📝

👤

Show us your "About Me" program!

🎨

What creative outputs did you make?

🔧

Did you practice escape sequences (\n, \t)?

🐛

What bugs did you create and fix?

⚡ Quick Structure Quiz! ⚡

Let's test your Session 3 memory!

🔍 What does #include <stdio.h> do?

🚪 Where does every C program start?

🎯 What does \n do in printf?

✏️ What punctuation ends every statement?

💬 How do you write comments in C?

🎯 Today's Epic Mission! 🎯

📦 Learn what variables are and why we need them

🎭 Discover the main data types: int, float, char

🧠 Understand how computer memory works

📝 Learn to declare and initialize variables

🏷️ Master variable naming rules

🎨 Create programs that remember information

From static text to dynamic programs!

🤔 The Problem with Our Current Programs 🤔

printf("My age is 13");
printf("My height is 5.2 feet");
printf("My grade is A");
            

What if we want to:

🎂 Update our age when we have a birthday?

📏 Change our height as we grow?

📊 Calculate our grade average?

🔄 Use the same information multiple times?

We need a way to store and change information!

📦 What Are Variables? 📦

Think of variables as labeled boxes that store information!

age

13

integer

height

5.2

decimal

grade

A

character

🏷️ Named Storage

Each variable has a meaningful name

🔄 Changeable

Values can be updated anytime

🧠 How Computer Memory Works 🧠

Computer memory is like a giant apartment building with numbered addresses!

Memory Address: 1000

📦

Variable: age

Value: 13

Memory Address: 1004

📦

Variable: height

Value: 5.2

The computer knows exactly where to find each piece of information!

🎭 Meet the Big Three Data Types! 🎭

Just like we organize different types of items, C organizes different types of data!

🔢

int

Whole Numbers

13, 42, -7, 0, 1000

%d

🌊

float

Decimal Numbers

5.2, 3.14, -2.5, 0.1

%f

🔤

char

Single Characters

'A', 'z', '5', '@', ' '

%c

📝 How to Create Variables 📝

Declaration Syntax:

datatype variableName;

// Examples:
int age;
float height;
char grade;
            

Declaration + Initialization:

int age = 13;
float height = 5.2;
char grade = 'A';
            

🎨 Format Specifiers: Telling printf What to Expect 🎨

%d

For integers

printf("%d", age);

Output: 13

%f

For floats

printf("%f", height);

Output: 5.200000

%c

For characters

printf("%c", grade);

Output: A

%.1f

Float with 1 decimal

printf("%.1f", height);

Output: 5.2

💻 Let's Write Our First Variable Program! 💻

#include <stdio.h>

int main() {
    // Declare and initialize variables
    int age = 13;
    float height = 5.2;
    char grade = 'A';
    
    // Display the information
    printf("My age is %d years\n", age);
    printf("My height is %.1f feet\n", height);
    printf("My grade is %c\n", grade);
    
    return 0;
}
            

Let's type this together and see the magic happen!

🏷️ Variable Naming Rules & Best Practices 🏷️

✅ Valid Names

age
studentGrade
my_height
score2
_temp

❌ Invalid Names

2age (starts with number)
my-height (hyphen not allowed)
student grade (spaces not allowed)
int (reserved keyword)
@score (special characters)

🎯 Golden Rules:

Start with letter or underscore

Only letters, numbers, and underscores allowed

Case-sensitive (Age ≠ age)

Use meaningful names (age, not x)

Use camelCase or snake_case

🧠 Quick Variable Quiz! 🧠

Which variable declaration is CORRECT?

A)

int 2age = 15;

B)

float average = 9.5;

C)

char name = "John";

D)

int my-score = 100;

Type your answer in the chat!

🔄 Updating Variable Values 🔄

#include <stdio.h>

int main() {
    int score = 80;           // Initial value
    printf("Initial score: %d\n", score);
    
    score = 90;               // Update the value
    printf("Updated score: %d\n", score);
    
    score = score + 5;        // Math with variables
    printf("Final score: %d\n", score);
    
    return 0;
}
            

Variables are called "variable" because they can vary (change)!

🚨 Common Variable Mistakes to Avoid! 🚨

❌ Wrong Quotes for char

char grade = "A";

Fix: Use single quotes

char grade = 'A';

❌ Using Without Declaration

score = 100;

Fix: Declare first

int score = 100;

❌ Wrong Format Specifier

printf("%d", height);

Fix: Use correct specifier

printf("%f", height);

❌ Mixing Data Types

int age = 13.5;

Fix: Use correct type

float age = 13.5;

🎯 Your Turn: Personal Info Program! 🎯

Create a program that uses all three data types:

📊 Declare an int variable for your age

📏 Declare a float variable for your height

🎓 Declare a char variable for your favorite subject's first letter

🖨️ Use printf to display all three with proper format specifiers

🔄 Update one variable and print it again

// Example structure:
#include <stdio.h>

int main() {
    // Your variable declarations here
    
    // Your printf statements here
    
    return 0;
}
            

🏆 Look What You've Mastered! 🏆

📦 Understanding Variables

🎭 Three Data Types

🧠 Memory Concepts

📝 Declaration Syntax

🎨 Format Specifiers

🔄 Updating Values

Your programs can now remember and change information! 🎉

You've leveled up from static to dynamic programming!

🏠 This Week's Variable Adventures! 🏠

📝 Practice Assignments:

🎯 Complete the Personal Info Program - Use int, float, and char
🔄 Create an "Update Program" - Start with values, then change them
🎨 Make a "Family Info Program" - Store info about 3 family members
🧪 Experiment Challenge - Try different format specifiers (%.2f, %5d)
🐛 Bug Hunt - Intentionally make mistakes, then fix them

🚀 Next Week: Session 5

Input and Calculations

We'll learn how to ask users for information and do math with variables!

🤔 Think About This Week:

What information would you like your program to ask the user for?

🎉 Amazing work! You're now a variable master!