Classes

<aside> 💡 Formal Definition A ****class is a blueprint for creating objects (a particular data structure), providing initial values for state (member variables or attributes), and implementations of behaviour (member functions or methods).

</aside>

“Structs with functions!”

• By default, all struct members have a default access specifier of public
• Classes can have access specifier of public, private and protected

export struct student{
    int assn, mt, final; //fields of the receiver object
    float grade();
};

float student::grade(){  //a member function (or method) 
												 // :: called the scope resolution operator
    return assn * 0.4 + mt * 0.2 + final * 0.4;
}

//formally methods take a hidden extra parameter called (this) 
//-ptr to the reciever obbject

Student s {60, 70, 80} 
// Student => Class
// s => object

When we see C::f, it means f is the context of class C (the :: is called the scope resolution operator (C is either a namespace or class)

Q: what’s the difference between a method and a function?

Ans: Methods take a hidden extra parameter called this, which is a pointer to the receiver object

Initializing Objects

The following works

Student s{60, 70, 80}

But there is a much better way. We can use a constructor

<aside> 💡 Constructor is a method that initializes an object

</aside>

Here’s an implementation of it

struct Student {
	int assignment, midterm, final;
	float grade();
	Student (int assignment, int midterm, int final);
};

Student::Student(int assignment = 0, int midterm = 0, int final = 0) {
	this->assignment = assignment;
	this->midterm = midterm;
	this->final = final;
}

int main() {
	Student s{60, 70, 80}; 
	Student s = Student{60, 70, 80} // Alternative syntax (not-sementically identical??)

	Student s2{70, 80} // 70, 80, 0
	Student s3; // 0, 0, 0 (still calling the constructor!
}