Structures and Enumerations in C++

# CHAPTER 13

Structures and Enumerations #

1. Introduction #

2. Learning Objectives #

• Define and instantiate a struct.

• Access and modify structure members using the dot (.) operator.

• Understand nested structures.

• Create Arrays of structures.

• Use Enumerations (enum) to improve code readability.

3. Creating a Structure #

#include <iostream>
#include <string>
using namespace std;

// 1. Define the blueprint
struct Student {
    string name;
    int age;
    float gpa;
}; // ALWAYS end struct definitions with a semicolon!

int main() {
    // 2. Create an instance (variable) of the struct
    Student s1;

    // 3. Access members using the dot (.) operator
    s1.name = "Alice";
    s1.age = 20;
    s1.gpa = 3.9;

    cout << "Name: " << s1.name << " | GPA: " << s1.gpa << endl;

    return 0;
}

4. Arrays of Structures #

Student classList[3];

classList[0].name = "Alice";
classList[0].gpa = 3.9;

classList[1].name = "Bob";
classList[1].gpa = 2.5;

5. Pointers to Structures (-> Operator) #

Student s1;
s1.name = "Alice";

Student* ptr = &s1;

// Using the arrow operator to access a member through a pointer
cout << ptr->name << endl; // Prints "Alice"

6. Enumerations (enum) #

#include <iostream>
using namespace std;

// By default, Monday=0, Tuesday=1, Wednesday=2...
enum Day { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday };

int main() {
    Day today = Wednesday;

    if (today == Wednesday) {
        cout << "It&#039;s the middle of the week!" << endl;
    }
    
    // Enums are basically integers under the hood
    cout << "Today is day number: " << today << endl; // Prints 2

    return 0;
}

7. Modern C++: Scoped Enums (enum class) #

enum class Color { Red, Green, Blue };
enum class Fruit { Apple, Red, Banana }; // Perfectly valid!

Color carColor = Color::Red; // Must use the scope resolution operator ::

8. Mini Project: RPG Character Stats #

#include <iostream>
#include <string>
using namespace std;

struct Stats {
    int health;
    int mana;
    int attack;
};

struct Character {
    string name;
    string jobClass;
    Stats attributes; // Nested Structure!
};

int main() {
    Character hero;
    hero.name = "Arthur";
    hero.jobClass = "Knight";
    hero.attributes.health = 100; // Accessing nested members
    hero.attributes.mana = 20;
    hero.attributes.attack = 35;

    cout << "Hero: " << hero.name << " (" << hero.jobClass << ")\n";
    cout << "HP: " << hero.attributes.health << " | ATK: " << hero.attributes.attack << endl;

    return 0;
}

9. Memory-Level Explanation #

10. Common Mistakes #

• Forgetting the semicolon: Struct definitions must end with };. Forgetting this causes bizarre compiler errors on the next line.

• Dot vs Arrow: Using ptr.name instead of ptr->name when dealing with pointers to structs.

11. Exercises #

1. 1. Define a Rectangle struct with width and height. Write a function that takes a Rectangle as a parameter and returns its area.

1. 2. Define an enum class for TrafficLights (Red, Yellow, Green) and use it in a switch statement.

12. MCQ Quiz with Answers #

13. Interview Questions #

• Q: What is Structure Padding and Data Alignment in C++?

• Q: Explain the difference between enum and enum class (Scoped Enums).

• Q: In C++, is there any actual difference between a struct and a class? (Answer: Yes, the default access modifier for struct is public, while for class it is private. Otherwise, they are identical).

14. Summary #

15. Next Chapter Recommendation #