Solve the following code. Please give me justification that why program is giving the error

Question

#include<iostream>
using namespace std;
class Demo
{
int value;
public:
Demo(int v = 0) {value = v;}
void showMessage()
{
cout<<"showMessage() Function"<<endl;
}
void display()const
{
cout<<"display() Function"<<endl;
}
};
int main()
{
const Demo d1;
d1.showMessage();
d1.display();
return(0);
}

Answer 1

You cannot call non-const function with const object. However,
You can call const function, with non-const object.