C++ में Structure और Class में अंतर

The surprising truth

struct Point {
    int x;          // public by default - accessible directly
};

class Point2 {
    int x;          // private by default - NOT accessible directly
};

Point  p;  p.x  = 5;    // OK
Point2 q;  q.x  = 5;    // ERROR: 'x' is private

Proof: a struct doing everything a class does

#include <iostream>
using namespace std;

struct Student {                       // struct, not class!
    string name;
    int marks;

    Student(string n, int m) {         // constructor in a struct - valid!
        name = n; marks = m;
    }
    void display() {                   // member function - valid!
        cout << name << " scored " << marks << endl;
    }
};

int main() {
    Student s("Aman", 92);
    s.display();
    return 0;
}

Compiles and runs perfectly. If someone says "struct cannot have functions" — that is true for C, false for C++. Knowing this distinction clearly is exactly what interviewers check.

Second (smaller) difference: default inheritance

struct B1 : A { };      // means : PUBLIC A   (struct defaults public)
class  B2 : A { };      // means : PRIVATE A  (class defaults private)

Same rule, applied to inheritance: struct inherits publicly by default, class privately. In practice everyone writes public explicitly, so this rarely bites — but it completes the answer.

C struct vs C++ struct (where the confusion comes from)

When do C++ programmers actually use struct?

• struct — for plain data bundles with no rules to protect: a Point{x, y}, an RGB colour, a pair of values. "Everything open, come and use it."
• class — when data has rules and must be protected behind functions: BankAccount, Student with validation. "Data locked, use the official doors."
• Interview line: "Technically only default access differs; by convention, struct for passive data, class for objects with behaviour and invariants."