Test 1 Information
- Test 1 will be held Thursday, 09/21/2023 from 6-7:50pm.
– No make-ups will be given except for pre-approved absence or illness, and a written excuse from the Dean of Students or the Student Experience office or the RPI Health Center will be required.
– If you have a letter from Disability Services for Students and you have not already emailed it to ds_instructors@cs.rpi.edu, please do so ASAP. Shianne Hulbert will be in contact with you about your accommodations for the test. - Coverage: Lectures 1-6, Labs 1-3, and Homeworks 1-2.
- OPTIONAL: you are allowed two physical pieces of 8.5x11” paper, that’s four “sides”. We will not collect these electronically and we will not pre-print them, you will have to bring these notes pages yourself if you want them. We will check at the start of the exam that you do not have more than two pieces of paper for your notes!
- Bring to the exam room:
– Your Rensselaer photo ID card.
– Pencil(s) & eraser (pens are ok, but not recommended). The exam will involve handwriting code on paper (and other short answer problem solving). Neat legible handwriting is appreciated. We will be somewhat forgiving to minor syntax errors – it will be graded by humans not computers.
– Computers, cell-phones, smart watches, calculators, music players, etc. are not permitted. Please do not bring your laptop, books, backpack, etc. to the exam room – leave everything in your dorm room. Unless you are coming directly from another class or sports/club meeting.
Lecture 5 --- Classes II: Sort, Non-member Operators
- Classes in C++;
- Non-member operators
5.1 C++ Classes
-
Nuances to remember
- Within class scope (within the code of a member function) member variables and member functions of that class may be accessed without providing the name of the class object.
- Within a member function, when an object of the same class type has been passed as an argument, direct access to the private member variables of that object is allowed (using the ’.’ notation).
5.2 Operator Overloading
- When sorting objects of a custom class, we can provide a third argument to the sort function, and this third argument is a comparison function.
- What if we do not want to provide this third argument? The answer is: define a function that creates a < operator for objects of that class! At first, this seems a bit weird, but it is extremely useful.
- Let’s start with syntax. The expressions a < b and x + y are really function calls! Syntactically, they are equivalent to operator< (a, b) and operator+ (x, y) respectively.
- When we want to write our own operators, we write them as functions with these weird names.
- For example, if we write:
bool operator< (const Date& a, const Date& b) {
return (a.getYear() < b.getYear() ||
(a.getYear() == b.getYear() && a.getMonth() < b.getMonth()) ||
(a.getYear() == b.getYear() && a.getMonth() == b.getMonth() && a.getDay() < b.getDay()));
}
then the statement
sort(dates.begin(), dates.end());
will sort Date objects into chronological order.
- Really, the only weird thing about operators is their syntax.
- We will have many opportunities to write operators throughout this course. Sometimes these will be made class member functions, but more on this in a later lecture.
5.3 Questions
- Can you solve leetcode problem 905 with an overloaded operator <, and make this overloaded operator < a non-member function?
- Can you solve leetcode problem 905 with an overloaded operator <, and make this overloaded operator < a member function?
- Can you solve leetcode problem 905 with an overloaded operator <, and make this overloaded operator < a member function, plus make the definition of this member function outside of the class definition?
5.4 Copy Constructor
- A copy constructor is a constructor which is used to create a new object as a copy of an existing object of the same class.
- Copy constructors are automatically generated by the compiler if you do not provide one explicitly. However, if your class uses dynamic memory (which will be covered in next lecture), and you want a copy constructor, then you must write your own copy constructor.
- Copy constructors get called when you create a new object by copying an existing object using the assignment operator (=), or when you pass an object by value to a function.
- Still use the Date class as an example, if you have defined your own copy constructor whose prototype is like:
Date(const Date &other);
and when you have the following lines of code:
Date a;
Date b = a;
The first statement will call the default constructor, while the second statement will call the copy constructor.