Function call is ambiguous C++

To add to what Greg has said: when you call FindArea, you are passing it two integer values:

FindArea(rad, heigh)

The first definition accespts three parameters with the last one being optional, it matches:

int FindArea(int radius, int height, int Pi = 3.1415)

But ... the second definition can also take two integer parameters:

int FindArea(int radius, int Pi = 3.1415)

So the system isn't sure which one you meant to call, and won't compile your code unless it decided wrongly!

There are also other problems with your code:

int FindArea(int radius, int Pi = 3.1415)

Will give you a defaulted value for Pi of three - which will create some very odd circles ...
If you want to pass a floating point value, you need to define your function as accepting a floating point value - and you probably want to return a floating point value as well!

double FindArea(int radius, int height, double Pi = 3.1415)
    {
    return Pi * radius * radius * height;
    }
    
double FindArea(int radius, double Pi = 3.1415)
    {
    return 4 * Pi * radius * radius * radius / 3;
    }

In fact, that cures your problem as well - because now when you try to call your function like this:

FindArea(rad, heigh)

Only the first definition matches, so the call is no longer ambiguous.

But ... you have to ask yourself why are you passing Pi as a value at all? It's is a universal constant and really can't be changed! :laugh:

Try also

#include <iostream>
#include <memory>
#include <cmath>
using namespace std;

class Shape
{
public:
  virtual double getArea() = 0;
};

class Cylinder: public Shape
{
  double radius, height;
public:
  Cylinder(double radius, double height):radius{radius}, height{height}{}
  double getArea() override { return 2 * M_PI * radius * height; }
};

class Sphere : public Shape
{
  double radius;
  public:
  Sphere(double radius):radius{radius}{}
  double getArea() override { return 4 * M_PI * radius * radius;  }
};

int main()
{
  string choice;

  cout << "please enter s for sphere or c for cylinder\n";

  cin >> choice;

  unique_ptr<Shape> shape;

  if ( choice == "s")
  {
    double radius;
    cout << "please enter radius\n";
    cin >> radius;
    shape = make_unique<Sphere>( radius );
  }
  else if ( choice == "c")
  {
    double radius, height;
    cout << "please enter radius and height\n";
    cin >> radius >> height;
    shape = make_unique<Cylinder>( radius, height);
  }
  else
  {
    cout << "invalid choice\n";
    return -1;
  }

  cout << "the area of the shape is " << shape->getArea() << "\n";
}