Difference Between Structure and Class in C++

In C++, a structure works the same way as a class, except for the difference that members of a class are private by default and members of a structure are public by default. 

For example, program 1 fails in compilation but program 2 works fine, 

Program 1

C++

// C++ Program to demonstrate that
// Members of a class are private
// by default
#include <iostream>

using namespace std;

class Test {
    // x is private
    int x;
};

int main() {
    Test t;
  
    // compiler error because x
    // is private
    t.x = 20;

    return t.x;
}

Output:

./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp: In function 'int main()':
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp:10:9: error: 'int Test::x' is private
     int x;
         ^
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp:18:7: error: within this context
     t.x = 20;
       ^
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp:10:9: error: 'int Test::x' is private
     int x;
         ^
./cf03c8d1-d4a3-43ea-a058-fe5b5303167b.cpp:20:14: error: within this context
     return t.x;
              ^

Program 2:

C++

// C++ Program to demonstrate that
// members of a structure are public
// by default
#include <iostream>

using namespace std;

struct Test {
    // x is public
    int x;
};

int main()
{
    Test t;
    t.x = 20;

    // works fine because x is public
    cout << t.x;
}

Output

20

There is no other difference as structures support all features of a class like member methods, inheritance and virtual functions. The following is a summary of differences

S. No.	Class	Structure
1	Members of a class are private by default.	Members of a structure are public by default.
2	It is declared using the class keyword.	It is declared using the struct keyword.
3	It is normally used for Object Oriented Programming.	It also allows almost all features of a class, but is normally used for the grouping of different datatypes.

To know about the Difference between C structures and C++ structures refer to this article.

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