📝 Lesson 3: Data Types and Operators

Data Types: The Building Blocks

Think of data types as different kinds of containers. Just like you wouldn't store soup in an envelope or mail in a bowl, different types of data need different types of storage!

Why Different Data Types?

Using the right data type is like using the right tool for a job. You wouldn't use a hammer to cut paper or scissors to drive a nail!

Declaring and Using Variables

Declaring a variable is like putting a label on a container before filling it.

// Declaration: Creating the container
int age;           // Empty container for whole numbers
double price;      // Empty container for decimals
char grade;        // Empty container for single character
bool isPassed;     // Empty container for true/false
string name;       // Empty container for text

// Initialization: Filling the container
age = 21;
price = 49.99;
grade = 'A';
isPassed = true;
name = "Sarah";

// Declaration + Initialization: Create and fill at once
int score = 100;
double temperature = 98.6;
char initial = 'J';
bool isReady = false;
string city = "New York";

Memory Visualization

Each data type uses different amounts of computer memory, like different sized boxes in storage.

Type Conversion: Changing Containers

Sometimes you need to convert data from one type to another, like pouring water from a cup to a bottle. C++ handles this, but it requires careful attention to avoid data loss.

Arithmetic Operators: Math Operations

Operators are like mathematical tools that work with your data.

The Special Modulus Operator (%)

The modulus operator gives you the remainder after division. It's like dividing cookies among friends and seeing how many are left over!

Compound Assignment Operators

These are shortcuts for common operations, like speed dial on a phone!

int score = 10;

// Long way vs. Short way
score = score + 5;    // Long way
score += 5;          // Short way (same result!)

// All compound operators
score += 3;    // score = score + 3
score -= 2;    // score = score - 2
score *= 4;    // score = score * 4
score /= 2;    // score = score / 2
score %= 3;    // score = score % 3

Increment and Decrement Operators

These operators add or subtract 1, perfect for counting!

Comparison Operators: Making Decisions

These operators compare values and return true or false, like asking yes/no questions.

Logical Operators: Combining Conditions

Logical operators let you combine multiple conditions, like asking "Do you have milk AND eggs?" or "Do you want coffee OR tea?"

Practice Exercise: Calculator Program

#include <iostream>
using namespace std;

int main() {
    double a, b;

    // TODO: prompt for and read a, then b
    // TODO: print sum, difference, product, quotient
    // TODO: print the results of a > b and a == b

    return 0;
}

#include <iostream>
using namespace std;

int main() {
    double a, b;

    cout << "Enter the first number: ";
    cin  >> a;
    cout << "Enter the second number: ";
    cin  >> b;

    // Arithmetic operators
    cout << "Sum:        " << a + b << '\n';
    cout << "Difference: " << a - b << '\n';
    cout << "Product:    " << a * b << '\n';
    cout << "Quotient:   " << a / b << '\n';

    // Comparison operators yield a bool (1 = true, 0 = false)
    cout << "a > b?  " << (a > b)  << '\n';
    cout << "a == b? " << (a == b) << '\n';

    return 0;
}

#include <iostream>
using namespace std;

int main() {
    double num1, num2, result;
    char operation;

    cout << "Enter first number: ";
    cin  >> num1;
    cout << "Enter operation (+, -, *, /): ";
    cin  >> operation;
    cout << "Enter second number: ";
    cin  >> num2;

    if (operation == '+') {
        result = num1 + num2;
        cout << "Result: " << result << '\n';
    } else if (operation == '-') {
        result = num1 - num2;
        cout << "Result: " << result << '\n';
    } else if (operation == '*') {
        result = num1 * num2;
        cout << "Result: " << result << '\n';
    } else if (operation == '/') {
        if (num2 != 0) {
            cout << "Result: " << num1 / num2 << '\n';
        } else {
            cout << "Error: Division by zero!" << '\n';
        }
    } else {
        cout << "Unknown operator: " << operation << '\n';
    }

    return 0;
}

Common Mistakes to Avoid

Quick Reference Card

Challenge Exercise: Eligibility Checker

#include <iostream>
using namespace std;

int main() {
    int age, score;

    cout << "Enter your age: ";
    cin  >> age;
    cout << "Enter your score (0-100): ";
    cin  >> score;

    bool isAdult   = age >= 18;
    bool passed    = score >= 60;
    bool honorRoll = score >= 90;
    bool eligible  = isAdult && passed;

    cout << "isAdult:   " << isAdult   << '\n';
    cout << "passed:    " << passed    << '\n';
    cout << "honorRoll: " << honorRoll << '\n';
    cout << "eligible:  " << eligible  << '\n';

    return 0;
}

🎯 Quick Quiz

Summary

📚 Additional Resources

• cppreference — Fundamental types
• cppreference — Arithmetic operators
• LearnCpp — Introduction to fundamental data types

🚀 What's Next?

You now know how to store data and operate on it — but every program also needs to make decisions. In Lesson 4: Control Structures, you'll take the comparison and logical operators from this lesson and put them to work in if/else statements and switch statements to control the flow of your programs.