Thread: using constructor for simple c++ code

I want to write a simple c++ code that will calculate some data for me. Since I'm new with c++ and I want to work with constructors to learn how they work, I have a problem and don't know how to solve it.

Code:

#include <iostream>
 
using namespace std;
 
class calc {
   public:
      double setPro (double pro );
      double getPro( void );
      calc();  // This is the constructor
   private:
      double prozent;
};
 
// Member functions definitions including constructor
calc::calc(void) {
   cout << "Object is being created" << endl;
}
double calc::setPro( double pro ) {
   pro = prozent;
   cout<<prozent;
}
double calc::getPro( void ) {
   return prozent;
}


// Main function for the program
int main() {
   calc quanten;
 
  


   quanten.setPro(10); 
   
 
   return 0;
}

When I run the code, I get the number 1.79154e-307 which is probably the size of the integer. For the begining I simply want to display the number I handle the function setPro. (In this case it's 10)
Thanks for your help!

Yes you are right. I still don't understand why I need this lane. Why do I need a private variable (generaly) and why do I have to say prozent = pro? I just don't see the advantage of this methode.