Can you explain the reason for the error?

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C++

#include<iostream>
#include<string>
#include<cstdlib>
using namespace std;
class Shape
{
 private:
 int length;
 int width;
 public:
 Shape() //DEFAULT CONSTRUCTOR
 {
  this->length=0;
  this->width=0;
 }
 Shape(int length,int width) //PARAMETERIZED CONSTRUCTOR
 {
  this->length=length;
  this->width=width;
 } 
 void setLength() //SETTER FUNCTION FOR SETTING LENGTH
 { 
   int length=0;   
   cout<<"Enter the length for box:";
   cin>>length;
   this->length=length;
 }
 void setWidth() //SETTER FUNCTION FOR SETTING WIDTH
 {
  int width=0;  
  cout<<"Enter the width for box:";
  cin>>width;
  this->width=width;
 }
 int getLength()
 {
  return this->length;
 }
 int getWidth()
 {
  return this->width;
 }
 int area() //AREA FUNCTION THAT RETURNS THE AREA OF SHAPE OBJECT
 {
  return this->length*this->width;
 }
 int operator +(Shape &S2) // + OPERATOR OVERLOADING FOR ADDING AREAS OF TEO 
                           // SHAPE OBJECTS
 {
  return this->area()+S2.area();
 }
};
int main()
{
 Shape S1();
 Shape S2();
 //Shape S1(3,2);
 //Shape S2(3,4);
 S1.setLength();
 S1.setWidth();
 S2.setWidth();
 S2.setLength();
 cout<<"Area of shape box1:"<<S1.area()<<endl;
 cout<<"Area of shape box2:"<<S2.area()<<endl;
 cout<<"Addition of areas of box1 + box2:"<<S1+S2<<endl;
 return 0;   
}

TERMINAL IS GIVING THIS ERROR:
<pre>PS C:\Users\kk\Documents\C++ course\23k-7702> cd "c:\Users\kk\Documents\C++ course\23k-7702\" ; if ($?) { g++ question3.cpp -o question3 } ; if ($?) { .\question3 }
question3.cpp: In function 'int main()':
question3.cpp:65:5: error: request for member 'setLength' in 'S1', which is of non-class type 'Shape()'
S1.setLength();
^~~~~~~~~
question3.cpp:66:5: error: request for member 'setWidth' in 'S1', which is of non-class type 'Shape()'
S1.setWidth();
^~~~~~~~
question3.cpp:67:5: error: request for member 'setWidth' in 'S2', which is of non-class type 'Shape()'
S2.setWidth();
^~~~~~~~
question3.cpp:68:5: error: request for member 'setLength' in 'S2', which is of non-class type 'Shape()'
S2.setLength();
^~~~~~~~~
question3.cpp:69:34: error: request for member 'area' in 'S1', which is of non-class type 'Shape()'
cout<<"Area of shape box1:"<<S1.area()<<endl;
^~~~
question3.cpp:70:34: error: request for member 'area' in 'S2', which is of non-class type 'Shape()'
cout<<"Area of shape box2:"<<S2.area()<<endl;
^~~~
question3.cpp:71:47: error: invalid operands of types 'Shape()' and 'Shape()' to binary 'operator+'
cout<<"Addition of areas of box1 + box2:"<<S1+S2<<endl;
~~^~~
PS C:\Users\kk\Documents\C++ course\23k-7702>

What I have tried:

I am creating shape class objects with parametermized constructor my code works fine but when I create objects with default constructor compiler gives me error.