#include
using namespace std;
double rect_area(double length, double width = 0)
{
if(!width)
width = length;
return length * width;
}
int main()
{
cout << "10 x 5.8 rectangle has area: ";
cout << rect_area(10.0, 5.8) << '\n';
cout << "10 x 10 square has area: ";
cout << rect_area(10.0) << '\n';
return 0;
}