C++ · OOP: classes and constructors

This is the same idea as Python classes, with stricter rules:

• private: members can only be reached from inside the class, and the compiler enforces it. Python only has the _name convention.
• The constructor has the class’s name and no return type. The member initialiser list (: name_(n)) sets members before the body runs.
• A const member function promises not to modify the object, so you can call it on const objects.
• The destructor ~ClassName() runs automatically when the object goes out of scope. I’ll come back to this with RAII.

#include <iostream>
#include <string>

class Student {
public:
    Student(std::string name, int marks) : name_(std::move(name)), marks_(marks) {
        std::cout << "constructed " << name_ << '\n';
    }
    ~Student() { std::cout << "destroyed " << name_ << '\n'; }

    const std::string& name() const { return name_; }
    bool passed(int cutoff = 40) const { return marks_ >= cutoff; }
    void setMarks(int m) { if (m >= 0 && m <= 100) marks_ = m; }

private:
    std::string name_;
    int marks_;
};

int main() {
    Student a("Sahaj", 88);
    {
        Student b("Ravi", 35);
        std::cout << b.name() << " passed? " << b.passed() << '\n';
    }   // b destroyed here
    a.setMarks(150);                 // ignored by validation
    std::cout << a.name() << " passed? " << a.passed(90) << '\n';
}

Output:

constructed Sahaj
constructed Ravi
Ravi passed? 0
destroyed Ravi
Sahaj passed? 0
destroyed Sahaj