A Default constructor is that will either have no parameters, or all the parameters have default values. If no constructors are available for a class, the compiler implicitly creates a default parameterless constructor without a constructor initializer and a null body.

  #include <iostream.h>
  class Defal 
    { 
       public: 
         int x; 
         int y;   
         Defal(){x=y=0;}
    };   
  int main() 
     {   
       Defal A;         
       cout << "Default constructs x,y value::"<<
            A.x <<" , "<< A.y << "\n"; 
       return 0; 
     }

    Default constructs x,y value:: 0,0

In the above example a default constructor has the default value of "0" for both the parameters.