Constructor with a single argument makes that constructor as conversion ctor and it can be used for type conversion.
public: Boo( int i );
Boo BooObject = 10 ; // assigning int 10 Boo object
Class can have a public method for specific data type conversions.
Boo(int i )
double i = BooObject;
// assigning object to variable i of type double.
now conversion operator gets called to assign the value.