Session 3: Variables and Data Types

Learning Objectives

• Understand what variables are and why we need them
• Learn different data types in C++
• Practice declaring and using variables

Warm-up (5 minutes)

In your mad libs program, you used variables like string adjective. Why do you think we need to tell the computer it’s a “string”?

New Concept Introduction (20 minutes)

What are Variables?

Variables are like labeled boxes where we store information:

• The label is the variable name
• The box type determines what kind of data it can hold
• The contents are the actual data

C++ Data Types

Text Data:

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string name = "Alice";      // Text (multiple words need special handling)
char grade = 'A';           // Single character

Number Data:

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int age = 15;               // Whole numbers
double price = 19.99;       // Decimal numbers
float temperature = 98.6f;  // Decimal numbers (less precise)

True/False Data:

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bool isStudent = true;      // Can only be true or false

Variable Declaration and Initialization

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// Declaration only
int score;

// Declaration with initialization
int score = 100;

// Multiple variables of same type
int x, y, z;
int a = 1, b = 2, c = 3;

Variable Naming Rules

• Must start with letter or underscore
• Can contain letters, numbers, underscores
• No spaces or special characters
• Case sensitive (age and Age are different)

Good names: playerScore, user_name, isGameOver Bad names: x, data1, thing

Hands-on Practice (25 minutes)

Exercise 1: Variable Playground (10 minutes)

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#include <iostream>
using namespace std;

int main() {
    // Try each of these variable types
    string favoriteMovie = "Your favorite movie";
    char letterGrade = 'A';
    int birthYear = 2008;  // Adjust to your birth year
    double gpa = 3.8;
    bool likesC++ = true;
    
    // Print them all
    cout << "Favorite movie: " << favoriteMovie << endl;
    cout << "Grade: " << letterGrade << endl;
    cout << "Birth year: " << birthYear << endl;
    cout << "GPA: " << gpa << endl;
    cout << "Likes C++: " << likesC++ << endl;
    
    return 0;
}

Exercise 2: Age Calculator (15 minutes)

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#include <iostream>
using namespace std;

int main() {
    int currentYear = 2025;
    int birthYear;
    int age;
    
    cout << "Enter your birth year: ";
    cin >> birthYear;
    
    age = currentYear - birthYear;
    
    cout << "You are " << age << " years old!" << endl;
    
    return 0;
}

Challenge/Quiz (10 minutes)

Challenge: Personal Profile Generator Create a program that asks for and stores:

• Full name (string)
• Age (int)
• Height in feet (double)
• Favorite subject grade (char)
• Whether they like programming (bool)

Display all information in a nicely formatted profile.

Validation Prompt

```
I'm learning C++ and just completed Session 3. Here's my solution to the Personal Profile Generator challenge:

[PASTE YOUR CODE HERE]

The challenge was: Create a program that collects personal information using different data types and displays it as a formatted profile.

Please check if my solution:
1. Uses at least 4 different data types correctly
2. Has meaningful variable names
3. Gets user input and stores it properly
4. Displays the information in a clear format

If there are issues, please explain what's wrong and give me a hint to fix it (don't give me the complete solution).
```

What You Learned

• ✅ Different data types: string, int, double, char, bool
• ✅ How to declare and initialize variables
• ✅ Variable naming conventions
• ✅ Using variables in calculations

Next Session Preview

In Session 4, you’ll learn to work with numbers and mathematical operations in C++!