A structure in C++ is a user-defined composite data type that groups variables of different types under a single name.

Defining and Using a Structure

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

struct PersonData {
    string fullName;
    int yearsOld;
    int examScore;
} personThree; // Variable declared with the structure

int main() {
    // Method 1: Declare and initialize separately
    PersonData personOne;
    personOne.fullName = "Alex Johnson";
    personOne.yearsOld = 22;
    personOne.examScore = 95;
    cout << "Name: " << personOne.fullName << " Age: " << personOne.yearsOld << " Score: " << personOne.examScore << endl;

    // Method 2: Initialize during declaration
    PersonData personTwo = {"Jamie Smith", 21, 88};
    cout << "Name: " << personTwo.fullName << " Age: " << personTwo.yearsOld << " Score: " << personTwo.examScore << endl;

    // Method 3: Using the variable declared with the structure
    personThree.fullName = "Taylor Brown";
    personThree.yearsOld = 23;
    personThree.examScore = 72;
    cout << "Name: " << personThree.fullName << " Age: " << personThree.yearsOld << " Score: " << personThree.examScore << endl;

    return 0;
}

Array of Structures

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

struct Employee {
    string employeeName;
    int employeeId;
    double salary;
};

int main() {
    Employee staff[3] = {
        {"Robert Chen", 101, 55000.0},
        {"Lisa Wang", 102, 62000.0},
        {"David Kim", 103, 48000.0}
    };

    staff[1].employeeName = "Sarah Jones"; // Modifying an element

    for (int i = 0; i < 3; ++i) {
        cout << "ID: " << staff[i].employeeId
             << " Name: " << staff[i].employeeName
             << " Salary: $" << staff[i].salary << endl;
    }
    return 0;
}

Pointers to Structures

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

struct Product {
    string productName;
    float price;
    int stock;
};

int main() {
    Product item = {"Wireless Mouse", 29.99, 150};
    Product* itemPtr = &item;

    cout << "Product: " << itemPtr->productName
         << " Price: $" << itemPtr->price
         << " Stock: " << itemPtr->stock << endl;

    return 0;
}

Nested Structures

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

struct Date {
    int day;
    int month;
    int year;
};

struct Event {
    string eventTitle;
    string location;
    Date eventDate; // Nested structure
};

int main() {
    Event conference;
    conference.eventTitle = "Tech Summit";
    conference.location = "Convention Center";
    conference.eventDate.day = 15;
    conference.eventDate.month = 6;
    conference.eventDate.year = 2024;

    cout << "Event: " << conference.eventTitle
         << " at " << conference.location
         << " on " << conference.eventDate.month
         << "/" << conference.eventDate.day
         << "/" << conference.eventDate.year << endl;

    return 0;
}

Structures as Funciton Parameters

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

struct Measurement {
    double length;
    double width;
};

// Pass by value
void displayMeasureByValue(Measurement m) {
    m.length = 0.0; // Change does not affect original
    cout << "In function (value): Length=" << m.length
         << " Width=" << m.width << endl;
}

// Pass by address
void displayMeasureByPointer(Measurement* mPtr) {
    mPtr->width = 99.9; // Change affects original
    cout << "In function (pointer): Length=" << mPtr->length
         << " Width=" << mPtr->width << endl;
}

int main() {
    Measurement room = {10.5, 8.2};
    Measurement box = {3.0, 2.5};

    displayMeasureByValue(room);
    displayMeasureByPointer(&box);

    cout << "Main - room: " << room.length << ", " << room.width << endl;
    cout << "Main - box: " << box.length << ", " << box.width << endl;

    return 0;
}

Using const with Structure Pointers

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

struct Account {
    string username;
    int loginCount;
};

void printAccountData(const Account* accPtr) {
    // accPtr->loginCount = 0; // Error: cannot modify const data
    cout << "User: " << accPtr->username
         << " Logins: " << accPtr->loginCount << endl;
}

int main() {
    Account userAcc = {"dev_user", 42};
    printAccountData(&userAcc);
    cout << "Original login count unchanged: " << userAcc.loginCount << endl;
    return 0;
}

Practical Example: Classroom Management

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

struct Pupil {
    string pupilName;
    int testResult;
};

struct Instructor {
    string instructorName;
    Pupil classList[5];
};

void setupClassroom(Instructor staff[], int numInstructors) {
    string idLetters = "ABCDE";
    for (int i = 0; i < numInstructors; ++i) {
        staff[i].instructorName = "Prof_" + string(1, idLetters[i]);
        for (int j = 0; j < 5; ++j) {
            staff[i].classList[j].pupilName = "Student_" + string(1, idLetters[j]);
            staff[i].classList[j].testResult = (rand() % 61) + 40;
        }
    }
}

void showClassData(Instructor staff[], int numInstructors) {
    for (int i = 0; i < numInstructors; ++i) {
        cout << "\nInstructor: " << staff[i].instructorName << endl;
        for (int j = 0; j < 5; ++j) {
            cout << "  Pupil: " << staff[i].classList[j].pupilName
                 << " Score: " << staff[i].classList[j].testResult << endl;
        }
    }
}

int main() {
    srand(time(nullptr));
    Instructor faculty[3];
    int facultyCount = sizeof(faculty) / sizeof(faculty[0]);

    setupClassroom(faculty, facultyCount);
    showClassData(faculty, facultyCount);

    return 0;
}

Practcial Example: Sorting an Array of Structuers

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

struct GameCharacter {
    string charName;
    int healthPoints;
    string characterClass;
};

void sortCharacters(GameCharacter roster[], int count) {
    for (int i = 0; i < count - 1; ++i) {
        for (int j = 0; j < count - i - 1; ++j) {
            if (roster[j].healthPoints > roster[j + 1].healthPoints) {
                GameCharacter swapTemp = roster[j];
                roster[j] = roster[j + 1];
                roster[j + 1] = swapTemp;
            }
        }
    }
}

void displayRoster(GameCharacter roster[], int count) {
    for (int i = 0; i < count; ++i) {
        cout << "Name: " << roster[i].charName
             << " HP: " << roster[i].healthPoints
             << " Class: " << roster[i].characterClass << endl;
    }
}

int main() {
    GameCharacter party[5] = {
        {"Arthas", 85, "Paladin"},
        {"Sylvanas", 70, "Ranger"},
        {"Thrall", 92, "Shaman"},
        {"Jaina", 68, "Mage"},
        {"Illidan", 95, "Demon Hunter"}
    };

    int partySize = sizeof(party) / sizeof(party[0]);
    sortCharacters(party, partySize);
    displayRoster(party, partySize);

    return 0;
}