OOP Code - Unfinished

#include <iostream>
using namespace std;

const float PI = 3.14159;
enum _Shape { square=1, rectangle, triangle, circle } ;     //Enum variable declaration and intilization.

// Main class to cover all shapes
class Shapes {
    int choice;
    int _s1, _s2, _s3;      //Sides of shape.
    int _b, _h;             //Base and Height of a Triangle.
    float _r;               //Radius of Circle.
public:
    // Area Calculation based on parameters
    float area () {
        switch (choice) {



        }
    }


};

// Simple function for printing Menu Lists.
void printMenu() {
    cout << "Welcome to OOP Principles!\n";
    cout << "Please choose a shape from the below list:\n\n";
    cout << "["<< square    << "] Square.\n";
    cout << "["<< rectangle << "] Rectangle.\n";
    cout << "["<< triangle  << "] Triangle.\n";
    cout << "["<< circle    << "] Circle.\n";
    cout << "";
}

void main () {
    bool loop = true;       //For do-while checking
    do {
        printMenu();
        cin.get();
    } while (loop);

}