What is constructor in c++,default and argument constructor

Constructer without any argument (default constructor).

       Let name of class is “list” and “size” and “fill” are two data members(variables) and "arr" is array  in a class then constructor without argument will be                                                           

list :: list()

 {             size=10;

arr=new int [size];

             fill=-1;

 }

Here we give values to size=10, and fill=-1, this is a default constructer,

Constructer with one parameter.

Let name of class is “list” and “size” and “fill” are two data members (variables) and "arr" is array in a class then constructor with one argument will be

list :: list(int num)

 {            size=num;

             arr=new int [size];

             fill=-1;

 }