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description title ms.date ms.topic author ms.reviewer
Learn how to handle Object Oriented
Object Oriented
05/11/2023
conceptual
fejo-git
---

Object Oriented

syntax class

object type / class: car instance: the car, that is in my garage. property: color green, 4 doors, shock absorber defective methods: drive, smoke, noise

class Car {

public:
 std::string brand;
 int ps;

void printcar() {
 std::cout << brand << " : " << ps;
}
};

int main() {

Car C;
C.brand = "bmw";
C.ps = 330;

Car C2;
C2.brand = "mercedes";
C2.ps = 330;

C.printcar();
C2.printcar();
}

constructor

Is always executed whenever a new instance is created.

class Car {
public:
 std::string brand;
 int ps;

Car(std::string brandP, int psP) {
 brand = brandP;
 ps = psP;
 std::cout << "Ein neues Auto wird erstellt" << std::endl;
}
void printCar() {
 std::cout << brand << " : " << ps << std::endl;
}
};

int main() {
Car c ("bmw", 330);
Car c2("mercedes", 330);

c.printcar();
c2.printcar();
}

The constructor enforces the input of a brand and horsepower.

encapsulation private methods

class Car {
private:
 std::string brand;
 int ps;

public:
 Car(std::string brandP, int psP) {
        brand = brandP;
        ps = psP;
        std::cout << "A new car is being created." << std::endl;
 }
 void tune() {
        ps += 20;
 }
 void printCar() {
        std::cout << brand << " : " << ps << std::endl;
 }
};

int main() {

Car c("bmw" , 330);
Car c2("mercedes", 330);

c2.tune();

c.printCar();
c2.printCar();
}

// output:
//A new car is being created.
//A new car is being created.
//bmw : 330
//mercedes : 350

Variables and methods marked as 'private' can only be modified or accessed within the Car class.

keyword this

class Car {
private:
 std::string brand;
 int ps;
public:
 Car(std::string brand, int ps) {
            this->brand = brand;
            this->ps = ps;
            std::cout << "Ein neues Auto wird erstellt" << std::endl;
 }
};

"The 'this' keyword accesses the variable in 'private' and not the passed parameter. Within a class, 'this' is used to access class properties, while from outside, it's accessed with 'c.printCar()'."

getter and setter

GET-method or GETTER

std::string getBrand() {
    return brand;
}

int getPs() {
    return ps;
}

SET-methods or SETTER

void setPs(int ps) {
    if(ps > 1000) {
            std::cout << "Thats not possible!" << std::endl;
    }
    else {
            this->ps= ps;
    }
}

Both methods must be defined within the class.

int main() {

c.setOs(307);
std::cout << c.getBrand() << std::endl;
std::cout << c.getPs() << std::endl;
}

Main program to call the two set and get methods.

See also