Const in CPP

• Declaration of const data member
  const int x = 10;

• once you have initialized x you can not reassign its value

• value can not be changed

• initialization is not same as assignment
  const int x = 20; //initialization
  x = 20; // assignment

• example of constant value is pi = 3.14

• we can initialize const members from both inside and outside of class

• We can initialize const variable from outside of the class also, like passing value from main as parameter

• Initializer list is used to define const members from outside of the class

• How to initialize const data member outside of a class

• for that you must use initializer list
  

#include <iostream>

using namespace std;

class A{
    public:
    const int a;
    // A(int b){
    //     a = b;
    // }

      A(int b) : a(b) {}; //initializer list

    void show(){
        cout<<a;
    }

// void changename(){
  //   a = 45;   
    //}
//error: assignment of read-only member ‘A::a’
};

int main()
{
    A obj(5),obj2(6);
    obj2.show();
    obj.show();

    return 0;
}

//output : 65