Classes and objects

Why do we need different data structures?

Different data structures have advantages and disadvantages. There is no best data structure that can fit the need of all applications.

Data structures can be compared along multiple dimensions, such as time complexity: time needed to complete certain tasks and memory consumption
If you need time to program customized data structure, you may also need to consider implementation difficulty. In practice a programmer needs to evaluate the pros and cons of different data structures and choose or make the one that best fits their needs in the specific task.
The results of using different data structures may not be very significant for small projects but can be substantially different in large scale projects with large data.

Algorithm: Finite sequence of unambigious instructions performed to achieve a goal or compute a desired result.

Each algorithm is not a solution, but instead a precisely defined procedure for deriving solutions.

Each algorithm should specify each of the following:

Name and purpose
Input and output
Unambigously specified finite sequence of steps
Termination condition or terminating state

Write the code to return the sum of 1, 2, 3, ...n

For Loop Version

#include <iostream>
using namespace std;

int main() {
    int n =4; //can change the value of n here, define an integer
    int result = 0; //to store the result, initial value is zero
    
    
    for (int i=1; i<=n; i++){ //For each integer from 1 to n, add their values to result
        result = result +i;
    }
    return 0;

    cout << "The result is:" << result << endl; //Output the value of result
}

Switch Case Version

#include <iostream>
int main() {
    int n = 4; 		// can change the value of n here.
    int result = 0; 	// to store the result, initial value is zero.
    // Unambiguously specified finite sequence of steps below

    switch (n){
        case 0: result = 0;
            break;
        case 1: result = 1;
            break;
        case 2: result = 3;
            break;
        case 3: result = 6;
            break;
        case 4: result = 10;
            break;
        default:
            std::cout<<"Error! I did not consider this yet. "<<std::endl;
            break;
    }

    std::cout<<"The result is: "<<result<<std::endl;
    return result;
}

Math Equation Version

#include <iostream>
int main() {
    int n = 4; 		// can change the value of n here.
    int result = 0; 	// to store the result, initial value is zero.
    // Unambiguously specified finite sequence of steps below

    result = n * (n+1) / 2;

    std::cout<<"The result is: "<<result<<std::endl;
    return result;
}

Data Structure: A coherent organization of related data items for efficient storage and usage, and methods that operate on the data items.

Car Struct

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

struct Car {
    //all members are public by default
    int year;
    string brand;
    double price;
};

int main() {
    Car carInventory[100];

    //add car 1
    carInventory[0].year = 2002;
    carInventory[0].brand = "Honda";
    carInventory[0].price = 1000.00;

    //add car 2
    carInventory[1].year = 1984;
    carInventory[1].brand = "Porsche";
    carInventory[1].price = 40000.00;

    //print all
    cout<<"The first car is: " << carInventory[0].year << " " << carInventory[0].brand << ", price: " << carInventory[0].price<< endl;
    cout<<"The second car is: " << carInventory[1].year << " " << carInventory[1].brand << ", price: " << carInventory[1].price<< endl;

    return 0;
}

What's the problem with procedure based programming? - not well organized, data is not protected, okay for a small project in which you're the only user.

Every other function can directly access and modify other variables in structures.

Procedure Oriented Programing

All data items and structures are public
A procedure using fucntions to process the data
They may be accidentally affected
Big problem when many programmers working on the same project

Object Oriented Programming

Allows a data structure's members to be private
Methods(functions) that operate on these data items are includewd within the data structure
Users of the data structure use the public methods to achieve their goals, without accidentally affecting the priate data items in any bad ways
This is called encapsulation

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

struct Car {
    //all members are public by default
    int year;
    string brand;
    double price;
};

class CarRecord {
    //all members are private by default
    Car carInventory[100];
    int size = 0;

public:
    void addCar (int year, string brand, double price);
    void printAll ();
};

void CarRecord::addCar(int year, string brand, double price) {
    carInventory[size].year = year;
    carInventory[size].brand = brand;
    carInventory[size].price = price;
    size++;
}

void CarRecord::printAll() {
    for (int i = 0; i < size; i++){
        cout<<"Car #" << i << ": " << carInventory[i].year << " " << carInventory[i].brand << ", price: " << carInventory[i].price<< endl;
    }
}



int main() {
    CarRecord inventory;

    //add car 1
    inventory.addCar(2002, "Honda", 1000.00);

    //add car 2
    inventory.addCar(1984, "Porsche", 40000.00);

    //print all
    inventory.printAll();

    return 0;
}

Class and Object

In object oriented programming,

a class represents a kind of objectsl it is a template for creating instances of specific objects; it is an abstraction of the things that are common to the kind of objects.
an object represents an indivdual and specific item; it is an instance of the general class

Summary

Algorithm: Sequence of clear instructions to achieve a goal

Data Structure: Data items and related methods about the same object.

By default, a variable member of a class in C++ is private

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